This Karcher K3.550 is above the base models being water cooled with a maximum pressure of 120Bar.
Assembly is required but if you can think enough about pressure washers to buy up to this one, then the assembly will not task you. It has an on board detergent tank with a variable dispensing rate.
Just spotted this in Argos at £133.32 if wanted pronto.
Free delivery so save your fuel costs, I did.