Phone Mark One Hire in Rayleigh. They hire the generators out. Tell em you want to hire one to power a car jetwash and ask them what CC/size the generator is! The smallest ones are 2.7kw (you can get smaller elsewhere I think) and im sure that will be fine as i use this size when trading at shows (powering PC/Printer/Cutter/Air Compressor etc..)

HTH
Chris