Wireless,
Why not go into a couple of local high street banks and building societies, and ask them for their advice? Since Nationwide has specifically been mentioned has having a USD account, make sure that you include them in your selection. With the amount of money you're talking about, any bank should be happy to provide you with an adviser who will spend some time finding out exactly what you plan on doing with the money, and who will know what the best option is that their bank can offer you. If you really are as "rubbish at financial things" as you say you are, the adviser will be to explain exactly what is required, sort out any jargon, offer you reassurance and so on.
FFF
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