If you don't mind paying top price then pay on the day, otherwise book ahead

We live about one hour 45 minutes from Manchester airport on a good run. After a transatlantic flight , it is often the case that one of us is unable to finish the drive home and the other has to take over . This is in circumstances where we know the road, know where the destination is, know the car and we are driving on a familiar side of the road.
The person not driving is always asleep!

Alan is right - the earlier you book, the cheaper. Not sure when you're travelling but train tickets usually go on sale 3 months ahead. There are various websites you can use and I'm not aware of any difference - I usually use ww.thetrainline.com. I'd check flight prices too, though, as it can be just as cheap. Thinking about it, though, I'd only recommend bmi and not jet2, as the latter is a no-frills outfit which wouldn't help if your flight in was delayed & you missed their flight. bmi would just put you on the next flight.