Hi,
There are some ways to get a USA bank account when in the UK via some institutions offering accounts like that. You'll need to look around to see what might suit you.
If you are wanting mainly to have a direct US account, then the next time you go to the USA you can open up an account within 20 minutes. I'm a UK citizen and that's what I did on my last USA visit - opened 3 accounts, Bank of America, Wells Fargo & Chase. At each branch, it took around 30 minutes or so. This will give you a total USA based bank account. I vaguely recall that they do/did make a note of me being a UK citizen and had the right note on the account as well as giving me one that was easier to manage and be eligible for (I think the BoA account is an online one that best suits people like myself and others)
It's much more difficult to open a direct USA bank account when you are abroad, there's various places 'promising' to open one for you in this way and I looked into them for a short while. When I booked a visit, I just thought I'd try whilst in the USA first and easily opened the accounts in branch, so I have no idea if those places offering to open one up whilst out of the USA are good or not.
Cheers, DtM! West London & Slough UK!