Hmm, I am tending to agree with Gromit on parts of this.
AWS does not keep the data in the UK, it quite clearly states backups will be in the USA. Certain types of data should not be kept on foreign soil.
I worked at a UK Bank where we moved from AWS to Azure partly because of this. Another reason was that Azure was a heck of a lot cheaper plus being a platinum customer meant we good help.
//Who would you give the contract to//
Ideally the Home Office should have its own cloud. Its big enough and has a large enough budget. However with incompetence abounding and the inability to implement the simplest IT systems from the Civil Service, even when well over funded, I would opt for Azure.