Cash is an option. It's less common than in Europe, but 40 £20 notes are not that difficult to count or keep secure. If you are worried about security, you also need to worry about the "purchaser" just running off with the laptop without even pretending to pay.
It's almost entirely safe to give out your sort code and account number. You already do this if you ever write a cheque, for example.
There is a small risk that someone could set up a fraudulent direct debit in your name. But those can only be to organisations that accept direct debits so there's not much motive to do it, and you'd be able to reverse it as ...
First, check to see if the money is in Wells Fargo. If not, contact Wells Fargo.
Some banks have different branches with different codes, but the transfer might go through, properly, depending on the branch.