I think amounts vary as to the hotel and as to what's being done. My plan is to 'make amends' for all the past times! I tip a pound or two (easy with the coins) for luggage toting and getting a cab. At The Stafford the porter has to go down the street and hail a cab on St James and then ride it back up to the cul de sac where the hotel is located. It's not as if he just turns on a cab light or raises his hand. I also tip extra to the bar staff who tend to me very well, also not much. The other part of this is that it's a small hotel and I have somewhat of a personal relationship with the staff; they remember my likes and dislikes and what I drink. I think that merits a bit extra every so often.
Jane in PHL