I don't know whether or not this would be legal or practical, but could you set up two different companies?
Say:
Brighter Lights (Domestic) Window Cleaning
and
Brighter Lights (Commercial) Window Cleaning
The commercial can be registered for VAT and the other not registered. Why on Earth should regular Joes have to pay these iniquitous taxes?
I know of a landscape gardener near Luton who was planning the same strategy with the help of his accountant, but I lost touch with him so don't know how he got on.