GOV.UK Pay use Amazon ECS, not CF. They do this because it is PCI compliant. GOV.UK aren't quite yet entirely on AWS but are working toward that end. With GOV.

GOV.UK Pay use Amazon ECS, not CF. They do this because it is PCI compliant. GOV.UK aren't quite yet entirely on AWS but are working toward that end. With GOV.UK, all the code is in the open where possible (https://github.com/alphagov/govuk-aws https://github.com/alphagov/govuk-aws and https://github.com/alphagov/govuk-puppet https://github.com/alphagov/govuk-puppet respectively for the infrastructure). Source: I used to work at GDS.