diff --git a/app/dao/jobs_dao.py b/app/dao/jobs_dao.py
index e22c1c709..7cdca7da7 100644
--- a/app/dao/jobs_dao.py
+++ b/app/dao/jobs_dao.py
@@ -2,6 +2,7 @@ import uuid
 from datetime import datetime, timedelta
 
 from flask import current_app
+from notifications_utils.letter_timings import letter_can_be_cancelled, CANCELLABLE_JOB_LETTER_STATUSES
 from notifications_utils.statsd_decorators import statsd
 from sqlalchemy import (
     asc,
@@ -10,17 +11,23 @@ from sqlalchemy import (
 )
 
 from app import db
+from app.dao.dao_utils import transactional
+from app.dao.templates_dao import dao_get_template_by_id
 from app.utils import midnight_n_days_ago
+
 from app.models import (
     Job,
+    JOB_STATUS_FINISHED,
     JOB_STATUS_PENDING,
     JOB_STATUS_SCHEDULED,
     LETTER_TYPE,
     Notification,
     Template,
-    ServiceDataRetention
+    ServiceDataRetention,
+    NOTIFICATION_CREATED,
+    NOTIFICATION_CANCELLED,
+    JOB_STATUS_CANCELLED
 )
-from app.variables import LETTER_TEST_API_FILENAME
 
 
 @statsd(namespace="dao")
@@ -148,16 +155,35 @@ def dao_get_jobs_older_than_data_retention(notification_types):
     return jobs
 
 
-def dao_get_all_letter_jobs():
-    return db.session.query(
-        Job
-    ).join(
-        Job.template
-    ).filter(
-        Template.template_type == LETTER_TYPE,
-        # test letter jobs (or from research mode services) are created with a different filename,
-        # exclude them so we don't see them on the send to CSV
-        Job.original_file_name != LETTER_TEST_API_FILENAME
-    ).order_by(
-        desc(Job.created_at)
+@transactional
+def dao_cancel_letter_job(job):
+    number_of_notifications_cancelled = Notification.query.filter(
+        Notification.job_id == job.id
+    ).update({'status': NOTIFICATION_CANCELLED,
+              'updated_at': datetime.utcnow(),
+              'billable_units': 0})
+    job.job_status = JOB_STATUS_CANCELLED
+    dao_update_job(job)
+    return number_of_notifications_cancelled
+
+
+def can_letter_job_be_cancelled(job):
+    template = dao_get_template_by_id(job.template_id)
+    if template.template_type != LETTER_TYPE:
+        return False, "Only letter jobs can be cancelled through this endpoint. This is not a letter job."
+
+    notifications = Notification.query.filter(
+        Notification.job_id == job.id
     ).all()
+    count_notifications = len(notifications)
+    if job.job_status != JOB_STATUS_FINISHED or count_notifications != job.notification_count:
+        return False, "This job is still being processed. Wait a couple of minutes and try again."
+    count_cancellable_notifications = len([
+        n for n in notifications if n.status in CANCELLABLE_JOB_LETTER_STATUSES
+    ])
+    if count_cancellable_notifications != job.notification_count or not letter_can_be_cancelled(
+        NOTIFICATION_CREATED, job.created_at
+    ):
+        return False, "Sorry, it's too late, letters have already been sent."
+
+    return True, None
diff --git a/app/job/rest.py b/app/job/rest.py
index 20f37efed..145f3c004 100644
--- a/app/job/rest.py
+++ b/app/job/rest.py
@@ -13,7 +13,10 @@ from app.dao.jobs_dao import (
     dao_get_job_by_service_id_and_job_id,
     dao_get_jobs_by_service_id,
     dao_get_future_scheduled_job_by_id_and_service_id,
-    dao_get_notification_outcomes_for_job)
+    dao_get_notification_outcomes_for_job,
+    dao_cancel_letter_job,
+    can_letter_job_be_cancelled
+)
 from app.dao.fact_notification_status_dao import fetch_notification_statuses_for_job
 from app.dao.services_dao import dao_fetch_service_by_id
 from app.dao.templates_dao import dao_get_template_by_id
@@ -60,6 +63,17 @@ def cancel_job(service_id, job_id):
     return get_job_by_service_and_job_id(service_id, job_id)
 
 
+@job_blueprint.route('/<job_id>/cancel-letter-job', methods=['POST'])
+def cancel_letter_job(service_id, job_id):
+    job = dao_get_job_by_service_id_and_job_id(service_id, job_id)
+    can_we_cancel, errors = can_letter_job_be_cancelled(job)
+    if can_we_cancel:
+        data = dao_cancel_letter_job(job)
+        return jsonify(data), 200
+    else:
+        return jsonify(message=errors), 400
+
+
 @job_blueprint.route('/<job_id>/notifications', methods=['GET'])
 def get_all_notifications_for_service_job(service_id, job_id):
     data = notifications_filter_schema.load(request.args).data
diff --git a/requirements-app.txt b/requirements-app.txt
index 460c9bf4c..542c10758 100644
--- a/requirements-app.txt
+++ b/requirements-app.txt
@@ -29,6 +29,6 @@ awscli-cwlogs>=1.4,<1.5
 # Putting upgrade on hold due to v1.0.0 using sha512 instead of sha1 by default
 itsdangerous==0.24  # pyup: <1.0.0
 
-git+https://github.com/alphagov/notifications-utils.git@33.0.0#egg=notifications-utils==33.0.0
+git+https://github.com/alphagov/notifications-utils.git@33.1.0#egg=notifications-utils==33.1.0
 
 git+https://github.com/alphagov/boto.git@2.43.0-patch3#egg=boto==2.43.0-patch3
diff --git a/requirements.txt b/requirements.txt
index d3348afc0..0bc17e2d8 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -31,21 +31,21 @@ awscli-cwlogs>=1.4,<1.5
 # Putting upgrade on hold due to v1.0.0 using sha512 instead of sha1 by default
 itsdangerous==0.24  # pyup: <1.0.0
 
-git+https://github.com/alphagov/notifications-utils.git@33.0.0#egg=notifications-utils==33.0.0
+git+https://github.com/alphagov/notifications-utils.git@33.1.0#egg=notifications-utils==33.1.0
 
 git+https://github.com/alphagov/boto.git@2.43.0-patch3#egg=boto==2.43.0-patch3
 
 ## The following requirements were added by pip freeze:
-alembic==1.0.10
+alembic==1.0.11
 amqp==1.4.9
 anyjson==0.3.3
 attrs==19.1.0
-awscli==1.16.185
+awscli==1.16.188
 bcrypt==3.1.7
 billiard==3.3.0.23
 bleach==3.1.0
 boto3==1.6.16
-botocore==1.12.175
+botocore==1.12.178
 certifi==2019.6.16
 chardet==3.0.4
 Click==7.0
diff --git a/tests/app/dao/test_jobs_dao.py b/tests/app/dao/test_jobs_dao.py
index 524d17f8e..2a9cc8a4d 100644
--- a/tests/app/dao/test_jobs_dao.py
+++ b/tests/app/dao/test_jobs_dao.py
@@ -6,14 +6,16 @@ import pytest
 from freezegun import freeze_time
 
 from app.dao.jobs_dao import (
-    dao_get_job_by_service_id_and_job_id,
+    can_letter_job_be_cancelled,
+    dao_cancel_letter_job,
     dao_create_job,
-    dao_update_job,
-    dao_get_jobs_by_service_id,
-    dao_set_scheduled_jobs_to_pending,
     dao_get_future_scheduled_job_by_id_and_service_id,
-    dao_get_notification_outcomes_for_job,
+    dao_get_job_by_service_id_and_job_id,
+    dao_get_jobs_by_service_id,
     dao_get_jobs_older_than_data_retention,
+    dao_get_notification_outcomes_for_job,
+    dao_set_scheduled_jobs_to_pending,
+    dao_update_job,
 )
 from app.models import (
     Job,
@@ -308,3 +310,84 @@ def assert_job_stat(job, result, sent, delivered, failed):
     assert result.sent == sent
     assert result.delivered == delivered
     assert result.failed == failed
+
+
+@freeze_time('2019-06-13 13:00')
+def test_dao_cancel_letter_job_cancels_job_and_returns_number_of_cancelled_notifications(
+    sample_letter_template, admin_request
+):
+    job = create_job(template=sample_letter_template, notification_count=1, job_status='finished')
+    notification = create_notification(template=job.template, job=job, status='created')
+    result = dao_cancel_letter_job(job)
+    assert result == 1
+    assert notification.status == 'cancelled'
+    assert job.job_status == 'cancelled'
+
+
+@freeze_time('2019-06-13 13:00')
+def test_can_letter_job_be_cancelled_returns_true_if_job_can_be_cancelled(sample_letter_template, admin_request):
+    job = create_job(template=sample_letter_template, notification_count=1, job_status='finished')
+    create_notification(template=job.template, job=job, status='created')
+    result, errors = can_letter_job_be_cancelled(job)
+    assert result
+    assert not errors
+
+
+@freeze_time('2019-06-13 13:00')
+def test_can_letter_job_be_cancelled_returns_false_and_error_message_if_notification_status_sending(
+    sample_letter_template, admin_request
+):
+    job = create_job(template=sample_letter_template, notification_count=2, job_status='finished')
+    create_notification(template=job.template, job=job, status='sending')
+    create_notification(template=job.template, job=job, status='created')
+    result, errors = can_letter_job_be_cancelled(job)
+    assert not result
+    assert errors == "Sorry, it's too late, letters have already been sent."
+
+
+def test_can_letter_job_be_cancelled_returns_false_and_error_message_if_letters_already_sent_to_dvla(
+    sample_letter_template, admin_request
+):
+    with freeze_time('2019-06-13 13:00'):
+        job = create_job(template=sample_letter_template, notification_count=1, job_status='finished')
+        letter = create_notification(template=job.template, job=job, status='created')
+
+    with freeze_time('2019-06-13 17:32'):
+        result, errors = can_letter_job_be_cancelled(job)
+    assert not result
+    assert errors == "Sorry, it's too late, letters have already been sent."
+    assert letter.status == 'created'
+    assert job.job_status == 'finished'
+
+
+@freeze_time('2019-06-13 13:00')
+def test_can_letter_job_be_cancelled_returns_false_and_error_message_if_not_a_letter_job(
+    sample_template, admin_request
+):
+    job = create_job(template=sample_template, notification_count=1, job_status='finished')
+    create_notification(template=job.template, job=job, status='created')
+    result, errors = can_letter_job_be_cancelled(job)
+    assert not result
+    assert errors == "Only letter jobs can be cancelled through this endpoint. This is not a letter job."
+
+
+@freeze_time('2019-06-13 13:00')
+def test_can_letter_job_be_cancelled_returns_false_and_error_message_if_job_not_finished(
+    sample_letter_template, admin_request
+):
+    job = create_job(template=sample_letter_template, notification_count=1, job_status="in progress")
+    create_notification(template=job.template, job=job, status='created')
+    result, errors = can_letter_job_be_cancelled(job)
+    assert not result
+    assert errors == "This job is still being processed. Wait a couple of minutes and try again."
+
+
+@freeze_time('2019-06-13 13:00')
+def test_can_letter_job_be_cancelled_returns_false_and_error_message_if_notifications_not_in_db_yet(
+    sample_letter_template, admin_request
+):
+    job = create_job(template=sample_letter_template, notification_count=2, job_status='finished')
+    create_notification(template=job.template, job=job, status='created')
+    result, errors = can_letter_job_be_cancelled(job)
+    assert not result
+    assert errors == "This job is still being processed. Wait a couple of minutes and try again."
diff --git a/tests/app/job/test_rest.py b/tests/app/job/test_rest.py
index 03d4a289e..d81210491 100644
--- a/tests/app/job/test_rest.py
+++ b/tests/app/job/test_rest.py
@@ -71,6 +71,59 @@ def test_cant_cancel_normal_job(client, sample_job, mocker):
     assert mock_update.call_count == 0
 
 
+@freeze_time('2019-06-13 13:00')
+def test_cancel_letter_job_updates_notifications_and_job_to_cancelled(sample_letter_template, admin_request, mocker):
+    job = create_job(template=sample_letter_template, notification_count=1, job_status='finished')
+    create_notification(template=job.template, job=job, status='created')
+
+    mock_get_job = mocker.patch('app.job.rest.dao_get_job_by_service_id_and_job_id', return_value=job)
+    mock_can_letter_job_be_cancelled = mocker.patch(
+        'app.job.rest.can_letter_job_be_cancelled', return_value=(True, None)
+    )
+    mock_dao_cancel_letter_job = mocker.patch('app.job.rest.dao_cancel_letter_job', return_value=1)
+
+    response = admin_request.post(
+        'job.cancel_letter_job',
+        service_id=job.service_id,
+        job_id=job.id,
+    )
+
+    mock_get_job.assert_called_once_with(job.service_id, str(job.id))
+    mock_can_letter_job_be_cancelled.assert_called_once_with(job)
+    mock_dao_cancel_letter_job.assert_called_once_with(job)
+
+    assert response == 1
+
+
+@freeze_time('2019-06-13 13:00')
+def test_cancel_letter_job_does_not_call_cancel_if_can_letter_job_be_cancelled_returns_False(
+    sample_letter_template, admin_request, mocker
+):
+    job = create_job(template=sample_letter_template, notification_count=2, job_status='finished')
+    create_notification(template=job.template, job=job, status='sending')
+    create_notification(template=job.template, job=job, status='created')
+
+    mock_get_job = mocker.patch('app.job.rest.dao_get_job_by_service_id_and_job_id', return_value=job)
+    error_message = "Sorry, it's too late, letters have already been sent."
+    mock_can_letter_job_be_cancelled = mocker.patch(
+        'app.job.rest.can_letter_job_be_cancelled', return_value=(False, error_message)
+    )
+    mock_dao_cancel_letter_job = mocker.patch('app.job.rest.dao_cancel_letter_job')
+
+    response = admin_request.post(
+        'job.cancel_letter_job',
+        service_id=job.service_id,
+        job_id=job.id,
+        _expected_status=400
+    )
+
+    mock_get_job.assert_called_once_with(job.service_id, str(job.id))
+    mock_can_letter_job_be_cancelled.assert_called_once_with(job)
+    mock_dao_cancel_letter_job.assert_not_called
+
+    assert response["message"] == "Sorry, it's too late, letters have already been sent."
+
+
 def test_create_unscheduled_job(client, sample_template, mocker, fake_uuid):
     mocker.patch('app.celery.tasks.process_job.apply_async')
     mocker.patch('app.job.rest.get_job_metadata_from_s3', return_value={