diff --git a/app/main/forms.py b/app/main/forms.py
index b276f8215..823137497 100644
--- a/app/main/forms.py
+++ b/app/main/forms.py
@@ -40,6 +40,7 @@ from wtforms.validators import URL, DataRequired, Length, Optional, Regexp
 
 from app import format_thousands
 from app.main.validators import (
+    BroadcastLength,
     CommonlyUsedPassword,
     CsvFileValidator,
     DoesNotStartWithDoubleZero,
@@ -1324,6 +1325,7 @@ class BroadcastTemplateForm(SMSTemplateForm):
     def validate_template_content(self, field):
         OnlySMSCharacters(template_type='broadcast')(None, field)
         NoPlaceholders()(None, field)
+        BroadcastLength()(None, field)
 
 
 class LetterAddressForm(StripWhitespaceForm):
diff --git a/app/main/validators.py b/app/main/validators.py
index 104b4a932..8e091b0f7 100644
--- a/app/main/validators.py
+++ b/app/main/validators.py
@@ -7,6 +7,7 @@ from notifications_utils.recipients import (
     validate_email_address,
 )
 from notifications_utils.sanitise_text import SanitiseSMS
+from notifications_utils.template import BroadcastMessageTemplate
 from wtforms import ValidationError
 
 from app.main._commonly_used_passwords import commonly_used_passwords
@@ -120,6 +121,28 @@ class NoPlaceholders:
             raise ValidationError(self.message)
 
 
+class BroadcastLength:
+
+    def __call__(self, form, field):
+        template = BroadcastMessageTemplate({
+            'template_type': 'broadcast',
+            'content': field.data,
+        })
+
+        if template.content_too_long:
+            non_gsm_characters = list(sorted(template.non_gsm_characters))
+            if non_gsm_characters:
+                raise ValidationError(
+                    f'Content must be {template.max_content_count:,.0f} '
+                    f'characters or fewer because it contains '
+                    f'{formatted_list(non_gsm_characters, conjunction="and", before_each="", after_each="")}'
+                )
+            raise ValidationError(
+                f'Content must be {template.max_content_count:,.0f} '
+                f'characters or fewer'
+            )
+
+
 class LettersNumbersFullStopsAndUnderscoresOnly:
 
     regex = re.compile(r'^[a-zA-Z0-9\s\._]+$')
diff --git a/app/templates/views/edit-broadcast-template.html b/app/templates/views/edit-broadcast-template.html
index 8c5d7cfe9..21b0374d3 100644
--- a/app/templates/views/edit-broadcast-template.html
+++ b/app/templates/views/edit-broadcast-template.html
@@ -24,7 +24,7 @@
         }) }}
       </div>
       <div class="govuk-grid-column-two-thirds">
-        {{ textbox(form.template_content, highlight_placeholders=False, width='1-1', rows=5) }}
+        {{ textbox(form.template_content, highlight_placeholders=False, autosize=True, width='1-1', rows=5) }}
         {{ sticky_page_footer('Save') }}
       </div>
     </div>
diff --git a/requirements-app.txt b/requirements-app.txt
index da31bf0d3..a18e37063 100644
--- a/requirements-app.txt
+++ b/requirements-app.txt
@@ -24,7 +24,7 @@ Shapely==1.7.1
 awscli-cwlogs>=1.4,<1.5
 itsdangerous==1.1.0
 
-git+https://github.com/alphagov/notifications-utils.git@43.5.8#egg=notifications-utils==43.5.8
+git+https://github.com/alphagov/notifications-utils.git@43.6.0#egg=notifications-utils==43.6.0
 git+https://github.com/alphagov/govuk-frontend-jinja.git@v0.5.1-alpha#egg=govuk-frontend-jinja==0.5.1-alpha
 
 # gds-metrics requires prometheseus 0.2.0, override that requirement as later versions bring significant performance gains
diff --git a/requirements.txt b/requirements.txt
index 2f41e058e..f824f7542 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -26,7 +26,7 @@ Shapely==1.7.1
 awscli-cwlogs>=1.4,<1.5
 itsdangerous==1.1.0
 
-git+https://github.com/alphagov/notifications-utils.git@43.5.8#egg=notifications-utils==43.5.8
+git+https://github.com/alphagov/notifications-utils.git@43.6.0#egg=notifications-utils==43.6.0
 git+https://github.com/alphagov/govuk-frontend-jinja.git@v0.5.1-alpha#egg=govuk-frontend-jinja==0.5.1-alpha
 
 # gds-metrics requires prometheseus 0.2.0, override that requirement as later versions bring significant performance gains
diff --git a/tests/app/main/views/test_templates.py b/tests/app/main/views/test_templates.py
index 5560622c8..a45fcb06e 100644
--- a/tests/app/main/views/test_templates.py
+++ b/tests/app/main/views/test_templates.py
@@ -480,6 +480,7 @@ def test_broadcast_template_doesnt_highlight_placeholders(
         service_id=SERVICE_ONE_ID,
         template_id=fake_uuid,
     )
+    assert page.select_one('textarea')['data-module'] == 'enhanced-textbox'
     assert page.select_one('textarea')['data-highlight-placeholders'] == 'false'
 
 
@@ -1865,6 +1866,37 @@ def test_should_not_update_too_big_template(
     assert "Content has a character count greater than the limit of 459" in page.text
 
 
+@pytest.mark.parametrize('content, expected_error', (
+    (("ŴŶ" * 308), (
+        'Content must be 615 characters or fewer because it contains Ŵ and Ŷ'
+    )),
+    (("ab" * 698), (
+        'Content must be 1,395 characters or fewer'
+    )),
+))
+def test_should_not_create_too_big_template_for_broadcasts(
+    client_request,
+    service_one,
+    content,
+    expected_error,
+):
+    service_one['permissions'] = ['broadcast']
+    page = client_request.post(
+        '.add_service_template',
+        service_id=SERVICE_ONE_ID,
+        template_type='broadcast',
+        _data={
+            'name': 'New name',
+            'template_content': content,
+            'template_type': 'broadcast',
+            'service': SERVICE_ONE_ID,
+            'process_type': 'normal'
+        },
+        _expected_status=200,
+    )
+    assert normalize_spaces(page.select_one('.error-message').text) == expected_error
+
+
 def test_should_redirect_when_saving_a_template_email(
     client_request,
     mock_get_service_email_template,