I doubt it would save fuel - ultimately you're burning more fuel to heat the engine up more quickly, to save fuel. If it's to reduce engine wear, you're running the engine harder for a bit while it's cold to make it warm up faster, so I don't think you'll come out ahead from that perspective either. The only place it might help is if you simply can't get it to warm up, but I don't think it gets that cold in the UK?
I just installed a 120v one on mine, which I combine with a block heater. They're on a timer together, and turn on a little while before I get up in the morning.
