I was in Morrisons and saw they have the Power Devil 1400 power washer (for washing cars, patios etc)for £24.99. This price is £10 cheaper than Amazon. I suspect it is only avaliable instore. Nevertheless, at £25 for a power washer, it might be worth a trip to your local morrisons.
I've no idea how the quality of this washer compares with other power washers.
I'm also not sure if this is an offer - I think it might be their normal, though good, price.