Style changes: 2 important points still to be addressed

First bullet point needed a lead-in sentence. 

Removed the continuous integration link as there's nothing about C.I. there: /service-manual/agile/continuous-delivery.html
Crowdsourced as one word for consistency
All words in headers after the first word put in lower case
Load and performance testing not Load & performance testing

Still to do: define acceptance criteria. They're 1st mentioned in Features of agile, so explain the term there and link to it here. 
'Everyone is responsible for quality' this duplicates information in Quality. It only needs to be in 1 place and linked to from the other. https://www.gov.uk/service-manual/agile/quality.html - please decide where it should be.