Re Fidelity, I can’t trade US stocks on the platform! How backward are we over here 
Re Fidelity, try the US not the UK business. I have an account with them from my time over there but also opened one for my wife a couple of years ago and she’s never worked in the States.
Schwab might be the easier option as they have a London office.
“also opened one for my wife a couple of years ago and she’s never worked in the States.”
And she’s now the proud owner of a number of Berkshire shares.