ATM at Heathrow Airport

Fees can be charged by both the ATM and your bank, so much will depend on the latter. Typically bank-affiliated machines have lower fees than currency ATMs like Travelex. Also, which Terminal? You can look for ATMs on the Heathrow website (search for "cash machine" in the interactive map) https://www.heathrow.com/at-the-airport/terminal-facilities/cash-machines

Probably all ATMs at Heathrow will charge a fee, most are operated by Global Exchange and Travelex and will at least offer conversion and other services. If you decline any offers then you get cash at no additional exchange premium, just like any other ATM, just their fee of a few GBP, the 1% network fee, and whatever your bank charges. If you really need cash, then a few GBP will not ruin the trip.

You should be able to wait until you get into town, you really should not need any, if very little, cash. In town you will see lots of banks that offer "No ATM Fees", or at least used to. Many people travel for weeks in the UK and never use a pence. even the buskers on street corners have QR codes to drop them a Pound or two.

I had 20 pounds for a couple of years. Finally used it last month for the London Walks tour. London is very cash free IMHO

Unless you're buying illegal drugs you really shouldn't need cash. Even the stallholders at the primary school cake sale in my very rural corner of South West England have taken card for a few years now.

By all means get some cash for peace of mind but don't do it at Heathrow, those machines prey on uninformed people and are a bit of a disgrace.

Travelex lost the ATM contact at Heathrow some time ago so there are none in the public areas. However, the usage fee before getting into any other charges of the current operator (DC Payments) is generally £2.50. There are 2 Notemachine ATMs in the Terminals 2 & 3 tube station without an upfront fee.

However, as has already been said immediate cash is not a necessity for most.

Is there a reason you need cash? You certainly won't need it for transport or 99% of shops. If you do feel the need for cash, the airport is the last place to get some due to rip off rates. Wait until you reach an urban area an use an ATM in a bank or supermarket where you will get better rates and no fees.
Some small corner shop type stores still charge a fee for withdrawing, which has to be displayed by law, don't use them.

Thank you everyone for taking your time to answer our questions. I truly appreciate all of you. Happy Travels 🌸🌼🌺