If you have a Star Alliance Gold or Silver membership card, a number of special offers have been launched which can be redeemed at the new Terminal 2 at Heathrow. This is now home to all of the Star Alliance airlines, amongst others.
For Gold members, the best one is a free First Class upgrade on Heathrow Express.
You can redeem this as many times as you like up to May 31st. Note that you must be travelling on a full-fare Standard Class ticket which means that you cannot link it to the 12% discount for Mastercard holders which is currently available.
The other offers are valid for both Gold and Silver cardholders:
10% off at WH Smith when you spend £10
50% off Heathrow Meet & Assist
10% off Heathrow Valet Parking
50% off Heathrow Porter service
£20 off £100 spend at Thomas Pink
£10 off £150 spend at World Duty Free
free drink with a meal at The Gorgeous Kitchen
Apart from the Heathrow Express deal (which requires you to show your Star Alliance Gold card), the other offers are more flexible and it seems you only need to quote the relevant code.