Hard to say and alot depends on the firm. Average wage is between £14-£15k depending on the company. You can get more working for yourself but you have to start building up your business, which isn't the easiest. It's not mega money but man cannot live on bread alone. I'd rather do something I love than something I loathe.
Some companies pay peanuts and as a result alot of the lads do private work to supplement their incomes.
Don't be fooled by people telling you they make an annual salary treating wasp nests. They're a bonus, not a guarantee, and many people have come unstuck hoping