Get your OH to close the gas/electric accounts and reopen as joint accounts with British Gas. They will then start reporting payment history for you to credit agencies as well as for your OH, helping you to build credit from the start.
Apply for an American Express card before you leave. Once you are in the UK and after a short waiting period (can't remember now) you can transfer it to a UK credit card using your US credit history. AmEx isn't accepted in too many places but Amazon.co.uk and Argos both accept it. Use it occasionally otherwise AmEx won't report anything to the agencies.
Identify someone who can be a referee for your citizenship application in three years time.
Andy