Never heard of MegaTrain ? – They are part of the Stagecoach Group and sister firm MegaBus allowing you to travel on trains for just £1 per journey. Their website offers a wide range of cheap train tickets right across the UK.
UPDATED: Although many tickets are £1 please be advised a 50p booking feed with MegaTrain is applicable.
Find £1 tickets here: https://uk.megabus.com/megatrain.aspx
We tested a sample journey
Megatrain covers more or less the whole of the UK from London to Manchester, Glasgow to Bristol and everything in between.
We searched to find £1 tickets from Bristol to Manchester and we found several trains leaving on our chosen dates for just £1 and also some for £15.
Be prepared for a trawl though, because the Megatrain website is not easy to navigate.