Bletchley-Slough - Anytime Return 52.00, First Anytime Return 96.80 - almost twice as much. Outrageous given that you don't get a massive amount more than a slightly bigger seat/avoiding a bit of overcrowding if you're on 350s and Turbos.
In my view the multiplier should be 1.5 or 1.6 on the relevant Standard fare, including off-peak, as it tends to be in Europe. If it was I'd travel First a lot more often.
Neil
The largest price differential I've come across for First Class
over Standard Class is Oxenholme to Carlisle (VT / TPE). SVR* £16. FOR £101. Over 6x the price!
On the same route, the cheapest Standard Class VT 'Advance' fare costs £3, whereas the cheapest First Class VT 'Advance' fare costs £28. Over 9x the price. Crazy!
Milton Keynes to London, which is the same distance but on a busy commuter route, costs 'just' £72.40 for an FOR (2x FDS), and only £48 for an FOR restricted to Virgin Trains.
A similar, if not identical, situation occurs throughout Virgin Trains' network, such as Coventry to Milton Keynes. When the £16 SSR is valid, the cheapest available First Class ticket is still the £115 FOR. There are also very large price differentials between the Standard Class and First Class 'Advance' ticket tiers.
*The SVR is equivalent to the FOR because the SVR is unrestricted and there is no SOR or SDR.