CURRENTLY THE BEST PRICE FOR CUBES IN THE UK - KTC soya
This is the best price for a 20 litre cube with good availability in the UK (from a couple of hundred of us using it as fuel) with the exception of someone near Manchester selling 2 litre bottles with a lower per litre rate.
Easy to store, easy to keep in your car, and easier to pour than bottles.
Its soya which is not as good as rapeseed or sunflower - but its probably the one clocking up the most miles for vegetable oil in the UK. This is the box in a box and not the tin - which is slightly dearer although still a good price if no cubes are available (and you can wait to pour it through the tiny opening compared to the box).
Its Costco - so offline only.
DON'T TRY RUNNING ANY CAR ON VEGETABLE OIL UNLESS YOU KNOW ITS SUITABILITY.