My dad is/was a corgi reg plumber and hasn't bothered renewing as he is about to retire. However, one of the guys who used to work for me has set up on his own, still doing the odd bit of work for us.
He works very hard, starts at 6 in the morning on sites on a four day week - never home before 7 in the evening, and does a cash in hand central heating job Fri/Sat - him and his mate can do most houses in a day and a half to 2 days. He earns 85 - 90k per annum and just has the half costs of a van to run out of that. Never advertises - lives off recomendations