Boyfriend adding me to his bank account

I know it's sad, but after months of being in the UK, we have not put my name on the bank account we both use.  We want to go in tomorrow to get me on the account, and I was wondering what sort of documentation I should bring.  We are both American, and he banks with HSBC.  Is this going to be a nasty process, or should it be relatively simple?

Thanks!

It seems like everyone has a different experience when it comes to this. I would get your BF to phone his branch and check what they require.  It seems like most want to see your passport and some kind of proof of address like a utility bill. Hopefully you'll get someone who knows what they are doing and it will be simple! We had a bit of a palaver because we took in utility bill that we had just received and not yet paid. The person we were dealing with kept insisting she could not accept it as proof of address until we paid it!!! I asked to see the manager in the end and it got sorted out.

That doesn't sound too scary!  Couldn't make it in today anyway, I'll have him phone tomorrow.  Thanks!