A quick google and we also benefit from Norways gas too, I suppose thats one of the benefits of being a week later than the Nazis invading a country
I remember the gas lines being put in, I think one of the bases is down in Pembrokeshire along with the Oil refinery there.
The scale of Ratcliffe power station is impressive, and I know its the dirtiest fuel but Coal could be a short term answer. Its just not very flexible in terms of production, you can't just fire up a Coal powered power station then turn it off, thats why the French used to get electric for next to nothing from us in the night as we couldn't turn the stations off and had loads spare power in the grid.
We also apparently have more than double the amount of coal stock piled that we need to cease its use come 2025, so may as well use it in the pinch we find ourselves.