Stop at a Walmart and pick up a Buck 110 for $32. Coming to America and not buying a 110 is like going to Paris and not having a glass of wine.
Knife prices over the internet in the USA are very cheap in contrast to UK prices. If you buy from the same internet shops and have them shipped to the UK, your hit with very high shipping costs, import taxes and VAT. Pick out a few good knives and have them shipped to your friend's house and take them home in your checked luggage. Trust me you'll be the envy of all your friends at BBF.
Now I like going to a knife shop as much as the next person, but if I was visiting from the UK, I'd try and visit a pistol range. Ask your friend to try to find a local range. If he doesn't have a gun, most ranges have rental handguns for a few dollars plus the cost of ammo and targets.
have a great trip