ATMs at Heathrow

Only Travelex ATMs at Heathrow.

They tend to be Travelex machines, so check if there's a surcharge. You can find them on the airport map (search for cash machines):

https://maps.heathrow.com/

That said, I travel to London about six times a year, and use cash on average once or twice a year. So basically the norm is to pay by card. There's really no reason to withdraw cash, but if you do want it, maybe just withdraw a single £20 note once you're in the city - no need to do so at the airport. Avoid £50 notes as no one wants them.

Having looked through your previous questions, if you are still taking the Heathrow Express there are some NatWest ATMs at Paddington station.

but please take the note above seriously. Get the minimum you really need in cash - London and much of England is seriously no cash required, unless you want. There is one regular here who lives at the other end of the country and uses cash some.

I am an hour out of London and like the first poster I use cash of any sort once or twice a year. Everything else is tap and pay - be sure your cards have that.