Re: luton?
Update -
Took the tube in - cost £3.80 and took about 45 minutes, and I had to change to the Northern Line somewhere.
Took the Heathrow Express home - well worth the £14 if you are in any sort of hurry. Paddington is well linked by tube to everywhere else in central London.
It was scary how fast the whole thing was - I left the office (in Euston) at 17:00, walked about 3 or 4 minutes to the tube at Euston Square, got a tube almost immediately, changed at Paddington (2 or 3 minutes walk), got on the Express, got off at Heathrow, walked the obligatory few miles through the depths of the airport and was checked in by 17:35.
z