Prior to de-nationalisation (e.g. when I was travelling to and from college in the 1970s) BR charged �1 per reservation.. Given that you could buy 4 or 5 pints of beer for that amount in the early 1970s, it was a hefty fee.
When I used to travel for business purposes with GNER the charge was �1.00 each way....I believe the same route but different company are now charging �5.00 each way..