If I ever move to the U.K. I am going to start......
"The Undercutting Window Cleaning Co."
Get them to price it and we'll beat it
Seriously though wtf is the issue with undercutting, nearly everyone does it in every business that I am aware of. You pick your section of the market and you market to them. If you want the lower end you offer cheaper prices or discounts and if you want the more discerning end you add value and talk up the service.
Nothing wrong with " why pay more" imo if thats what you're after, but why not just extend your area a bit instead and leaflet or canvass if you want more work.