[tomatocracy]

The Heathrow Express used to have this at Paddington station, though I think it closed a while ago.

A similar idea which is available in London though is Airportr - this is a company which will send someone to collect your bags from your home/hotel and then inject them directly into the airport baggage system for you (if you're flying with the right airlines and checked in online). I've used it a few times and it's very good.