Some don't use diesel or petrol
Seen waiting to cross the Welshpool to Llanfair railway which is also steam, and yes there is a problem with fuel, it seems coal goes off once out of the ground, and the one remaining steam coal mine supplies one power station, when the power station closes so will the mine, even all the steam railways together don't use enough coal to keep it open.
There have been experiments to run steam trains on oil, mainly due to bank side fires, but expensive to run.
I suppose we will get fuel in local chemist as they did at the start, can shown was for sale at £250 empty so what will it cost full? But diesel is 35 sec gas oil, and is used for so much can't see that going, it may be the government will have to stop collecting tax on it. Petrol can be made in many ways, originally a paraffin, and two paraffins mixed together cetane and octane, CnH2n+2 I seem to remember from collage days, a variable compression ratio engine was calibrated using the two fuels then test fuel put in same engine and down to pre-ignition or pinking.
As it stands some unsafe practices are being allowed to promote electric cars, use of TN-C-S (PME) supplies is a problem and the safe touch voltage has been risen from 50 to 70 volt to allow EV charge points to be installed, the fire risk is also being swept under the carpet, it is a repeat of the diesel scenario where governments went flat out to promote diesel then realised an error.
I know my house only has a 60 amp supply, without oil fired central heating and diesel cars the supply likely needs to double to most houses. Can't see that happening in a hurry.