Most window cleaners offer windows,gutters conservatory and pressure washing.
If they dont, then maybe these are the type who run out of work or cant work on rainy days.
There is alot of money to be made pressure washing driveways and patios. I cant understand why 20 odd window cleaners in your area dont offer this service.....its madness
If I were you roger, I would buy a decent pressure washer and start earning extra dosh
Especially if the other guys dont do it.