I had an account with HSBC in 2007, and had no problems obtaining said account. However, having a US-based HSBC account wasn't any sort of requirement.
Where will you be living? I find I have to go into the bank more often here than I ever did for my banks in the US-- So, you may want to consider whether you'll have easy access to a CitiBank or not (there are only 4 in the UK, all in London)
People here have had a lot of luck opening accounts with Lloyds TSB, with just a US passport and proof of address. Another more recent post says this is also the case with NatWest.