Alan,
You appear to be making loads of dosh, you can afford it.

I asked this question once about dyeing carpets as when Rainbow started out that was their gimic.
I do not think there was much natural demand.
My new Catch Phrase is Niche Marketing, (read on the internet)
So I if you can find out who is likely to need this service, and prepared to pay a Premimum Price, and you can obtain Excellent Results you could have a Specialist Division and carry out work throughout the UK.
But once a lot of people know how to do it you cold be down to the odd job every know and then