I'm getting pretty p*****d off.
Of course you will. You're not an employee, mate, you work how YOU decide to work.
Why spend all that money on WFP + van and then use ladders?
Flip's sake!
Why don't you try to 'sell them' WFP - explain all the good points; it's safe, it cleans the frames lovely, there's no holes left in lawns, it's safe, it does a good job, it washes pvc doors down lovely, it's safe, it reaches those impossible to reach from ladders windows, and it's safe.
Did I say it was safe?
Ask them to give it a trail run or something; sell it. If they refuse to budge, walk away.