I think it’s the same as the official valet parking but basically at T5 you just follow the signs to valet parking, it takes you to a layby on check in level by T5 F check in. You drop your key off with the valet parking hut and off you go.
On return you do the same but in reverse except it’s in a car park on arrivals level (quick stop at hut to collect keys).
All v easy.
https://secure.heathrow.com/bav/?agent=BAVAL&src=PBAV01