I received an e-mail from GNER (they run trains to places like York and Edinburgh from London). They are testing a new website and are offering free first class tickets for anyone who buys a ticket. There are only 5000 available and I think you have to spend £15 - i have just booked mine. The site is at: http://tickets.gner.co.uk/gner/en/JourneyPlanning/GnerWebTISHomePage
It does say in the terms and conditions that you need to have recieved the e-mail from them but you never know it is worth a try (i have forward the e-mail to my mates and they are giving it a go). Even if you don't get a free ticket, you still get 10% off like on thier other site.
I used the button on the bottom left to find the cheapest fare available, very neat.
Just been on the site again to book some tickets for a friend as the offer is still open. However, I have noticed there are some £5 fares called 'Devil of an Offer' singles. They seem to have the same terms and conditions of normal cheap tickets (i.e. train specific no changes/refunds) but the have a funny name. Must be some promotion.
I had a quick look on thier other site and they are on there too, so it must be correct.
This offer has now finished - BUT there are a shed load of the £5 tickets available.