Yeah that's great mate, ta for the info

Good to know it could be used as a weekly thing and the solution is PH neutral. Would you put normal car shampoo in with the mixture? Main reason I'm considering one is for a more thorough clean for the bits you can't get to with a mitt, nooks and crannies, arches etc as having always owned older cars I'm paranoid about rust and salt is the enemy!
Seems to be an option of this as a proper lance for a pressure washer

or this for a garden hose although it seems to have mixed reviews from what I've been reading

Quite a lot of dosh for essentially a pressure washer attachment but if they do a good job, and if I can go halves with my stepdad I'm thinking it might possibly be worth the investment.