This isn't strictly a freebie as you would have to have purchased an airline ticket during the relevant period and you need to submit your boarding cards to NXEC so I guess it's a deal.
If you have travelled in EITHER direction (or both obv!) between either Glasgow (International only, not Prestwick) or Edinburgh and any of the London airports (Stansted, Luton, Heathrow, Gatwick, or City) on a weekday between 24/3/08 and 31/5/08, send your boarding cards to NXEC for a free first class return to/from any NXEC station north of Berwick and any NXEC station in England.
Obviously this is only any good if you hoard your boarding cards and it's limited to 2 per household but still a great deal, something for nothing nearly!
I remember Virgin Trains offering something sinilar a couple of years back. This was first seen in the Glasgow newspaper, the Evening Times. I was lucky, travelled GLA-LTN on March 24th! :) Two 1st class tickets with NXEC now in hand! :D
Note: Train travel must be reserved in advance 7 days before travel, last date for submission is 16/7/08, no restrictions on travel other than as above and general availability.
PS: As per point below, the flights can be either to or from London and a boarding pass is only required for one direction to qualify for the free return. Hope that's more clear, if not, click through the link to read the T&C or post a query for me on here.