The UK government office (Department of Pensions (I think that is the name)) to contact is in Newcastle. I'm not sure of the address or telephone number, but I'm sure it can be found on the Inland Revenue web site.
My dad gets his pension by direct deposit into his US bank account. If you are a legal resident alien and paid into a company pension or a government scheme, you will get something back regardless of where you live. My dad was not a British citizen when he worked here, I think he was on an ILR.
As an US citizen, if you have paid into Social Security, you will get part of it back (As long as it is not bankrupt in 30 yrs time
) no matter where you live.