That was during COVID, a lot of things closed then that were expected to reopen (BA MAN and NCL lounges too) I'm sure M&S at T5 is very successful.

I never see anyone using their Heathrow Rewards card there so just a reminder you can get points on all your purchases at Heathrow (so this includes the M&S, it's not just the expensive shops) and these can be converted to Avios (and other schemes) or used for shopping or parking vouchers. The only issue is the self service tills don't support it, so you have to ask the member of staff to add the points on when you show your receipt. If you use it frequently it can add up.

I doubt LHR will ever get a Greggs, so this is perfect to grab some food on the way out of the airport and I often pick up some wine too as well as food for the next day if I have nothing at home. It really is handy.