Don’t use plus to refer to VAT

Got some advice from the content community:

> I don't think we have a style on this - it doesn't really come up on
> GOV.UK mainstream.
>
> In your example, I'd go with something like 'less than £250 before
> VAT' or 'less than £250 (not including VAT)' to make it as clear as
> possible. Would that work?

I’ve gone with ’less than £250 (before VAT)’. I noticed that elsewhere
we’ve said ‘Each message costs 1.58 pence (plus VAT)’ so that feels
fairly consistent.

app/templates/views/pricing/how-to-pay.html

@@ -27,7 +27,7 @@
     </p>
 
     <p>
-      If the invoice is less than £250 +VAT, we’ll roll it into the next quarter’s invoice to save time and effort.
+      If the invoice is less than £250 (before <abbr title="Value Added Tax">VAT</abbr>) we’ll roll it into the next quarter’s invoice to save time and effort.
     </p>
 
     <p>
@@ -39,7 +39,7 @@
     </h2>
 
     <p>
-      If your organisation’s annual usage will cost over £500 +VAT you need to provide us with a purchase order so we can invoice you.
+      If your organisation’s annual usage will cost over £500 (before <abbr title="Value Added Tax">VAT</abbr>) you need to provide us with a purchase order so we can invoice you.
     </p>
 
     <p>