Power washers

fatrab

+1 for the Nilfisk. Watch out for lesser model Karcher's as they have plastic internals which fail, regularly. I'm on a car cleaning forum and Nilfisk have a far better reputation than Karcher.

road2manchester

Having owned a few pro washers, the DIY ones will never be great as the LPM (Litres per minute) tend to be low and therefore power not brilliant,

6-8 LPM even with a turbo nozzle and a short hose is a pain.All the manufacturers sell PSI (pounds per sq mtrs)..... means nothin.
The maths means to get high volume you need a bigger motor, biggest motor for 13 amp electrics is 2 horse power. That will work.

Petrol power may give you 12-18 lpm @ 1200 psi add a turbo nozzle and you can wash 120-160 mtrs a day easy.Also add 25 mtrs of hose Only issue the cost. I would rather hire one every year than but a Bosch, Karcher DIY one.

(Don't buy a cheap chinese imported one).

If you are cleaning moss from between the blocks etc look up CUBB WEED BRUSH