I can't speak for large hotel chains, but pubs and supermarkets only accept chip & pin cards now.
And small independents will not accept cards for purchases under £5 or even under £10 in some places.
Cash is king.
No idea what pickpocket rates are like in the US, but I've never been a victim in the UK myself. Not in London or the East Midlands. Although I admit I was taught to be wary from a very early age. For example it used to be a common trick to grab things from under the stall doors in public toilets. I've never lost the habit of hanging my bag on the hook inside the door, or if there isn't one, holding my bag on my lap. Nanny never put her bag on the floor
anywhere, simply so she could have it on her lap without worrying where it had been. Dani admired my pink bag, which I am very happy with. It seals via popper, zip and button. Short of actual bag-snatching, no-one is getting my purse without me knowing.
I feel like I'm carrying coals to Newcastle by saying this but check the internet re the best advice about changing money. You're coming at a bad time for the pound, sadly. For you I mean, it's strong at the moment.
Last time I went abroad it was weak and it served me better to withdraw money from a local ATM than change it in the UK. It would have been better to use a card for transactions but research suggested many places only took cash or had a surcharge. *this was in Amsterdam)
There are plenty of placs to change money at Heathrow, I just can't say what will leave you better off.
Having a choice of cash or card will give you more options on the Underground if you want to get a ticket from a machine. There will be a single queue which takes in 3-8 machines depending on the station; some are Card Only, some Cash and Card, some No Change Given (gah!)
Your route across town is a fairly easy one, but I'll break it down for you if you like, just ask.
Oh - best to have cash of you want to eat or drink on the train.
Card machines have a bad habit of breaking down mid-journey and you don't want to be stuck somewhere outside Peterborough with no way of buying a cup of tea
