Hmm!
If its quite now, what when the cuts hit!!!
I would try to add something else beside just Plumbing/gas fitting and heating to your repertoire of jobs you can do.
Funnily enough an employer can ask a Plumber to do work outside his or her trade, just so long as it is felt they are able to do it and they don't drop their wages.
That of course means they can ask you to do labouring jobs or painting.
Its up to the persons work you are doing to protest not you to refuse.
So hey guys and gals! How about gardening?
I would say that perhaps offering all in prices for set work may help as well.
Perhaps buy a load of showers cheap and offer a set price fitting service, people seem to want to know how much things are going to cost, before they ask you to do it.