They stopped these a while back,but have now returned from 14th July,just tried this out.
Glasgow to Birmingham 14th July return 22nd July £4.50.
But other dates I have found are from £1.50 single ie Glasgow /Birmingham a return 30th July to 6th August £2.00 return plus 50p booking fee = £2.50.....now that is cheap.
Or singles £1 plus 50p booking fee.
They have added other journeys too ie from Edinburgh,see website for journeys timetables available.
The trains you catch are run by Virgin trains and tickets only available for certain trains.
Just my luck I need to travel on the 10th July and it's going to cost me £30 single on normal train sites,this is how i came across this, I could'nt see it posted before.