If you go on the detailers forums - valeters with OCD ;-) - you'll find that the cheaper Karchers gat slated as the pump isnt very reliable and prone to break - plastic parts used where they use metal in the dearer models
The Nilfisk come highly recommended though and this one on Amazon is only a pound dearer - comes with car brush and patio cleaner.

https://www.amazon.co.uk/Nilfisk-X-Tra-Pressure-Washer-Cleaner/dp/B00AYBSQ4C

or if you prefer a patio thingy instead of a car brush...
Homebase K2 with patio thingy

Was a quid cheaper at Black Friday but still a good price.