The location of this flat is great, right in the middle of Mayfair. Unfortunately this was the only positive aspect of our stay.
48 hours before check in we were sent our check-in instructions, which involved picking the keys up from a location a full mile away from the flat. When traveling in a group with all of our luggage (and in the rain) this is not doable or acceptable. When we finally got to the flat, it was dirty with soot and hairballs on the floor and looked like it had not been vacuumed in weeks. When we called the service for it to be cleaned, the woman who answered was not helpful. They promised cleaners would come, and they never did.
A couple additional points for emphasis - the flat requires climbing 83 steps. The listing does note that it’s on the 4th floor, but I would emphasize that there is no lift and it’s not easy for older family members, and especially not with luggage.
The beds are tiny - UK doubles, possibly US full. I would not agree that that it sleeps 4 as at least one of the beds is much too small for two people.
This is a real shame because, as mentioned, the location is great and we wanted to love our stay. However, the combination of the above factors means we would certainly not stay here again. Very disappointed.