Ian, I have a similar background - I was a Business Manager in several main dealerships. Worked ridiculous hours, every weekend - practically missed the first 3 years of my sons life.
When I said I was leaving to clean carpets you could see the look in peoples eyes, thinking you must have a screw loose.
Fact of the matter is, whether your cleaning carpets, windows, or selling million pound properties - you're running a business, the fact that its cleaning windows is only incidental.