If you’re traveling into central London on an express train from Heathrow or Gatwick airports before June 30, 2007, you can upgrade to first class using the code BAUPGR. You’ll need to book your train tickets online by March 31, 2007 to score the deal.

The free upgrade translates into a savings of about 9GBP each way on express trains from Heathrow to Paddington or Gatwick to Victoria. Not bad. First class seats mean reclining chairs, free newspapers, work tables and refreshment service on trains from Gatwick and more legroom, free newspapers, continuous wireless service and disembarkation near the destination station’s exit on trains from Heathrow.

Here’s how to book, excerpted from the Business Traveller newsletter (linked below):

When taking the Heathrow Express you should collect your ticket(s) from one of the ticketing machines at the station, using either the eticket reference number or the credit card used to book the ticket.

The procedure for using Gatwick Express is easier. Passengers simply board the train and provide the reference number or show their credit card to the conductor.

Free First Class Upgrade for Airport Expresses