Nick Danter, 40, has been a full-time lecturer for 15 years and earns pound;25,000 as head of plumbing at Worcester College of Technology.

He remains committed to teaching even though he sees former students now earn pound;1,000 a week within months of qualifying. Mr Danter said: “I know I could be earning considerably more money outside teaching.

“If I was to work as a plumber or central heating engineer, which is what I did before going into teaching, I could easily increase my yearly salary by pound;15,000.

“One of my students who left last July earns pound;1,000 in a good week as a gas and plumbing engineer. That’s almost double my salary. It is very tempting. I know many people who’ve gone back, including staff from my own department.

“It’s not just the money that attracts them, it’s also less stressful in industry. We had one lecturer join us last year who thought teaching would be easy but, within three weeks, he wanted to get out because it was too much for him.

“Colleges have the flexibility to pay some lecturers more , according to demand, and I think they should. Since incorporation, colleges are supposed to act more like businesses. Well, in most businesses you could negotiate a pay rise if there is something much better elsewhere.”

So what keeps him in teaching? “I think it’s because we have great students. They come back every five years to keep up their qualified status and that keeps us in touch with them and the industry. It’s satisfying to see them thrive.”

Some plumbers are bucking the trend and leaving industry for colleges.

Kevin Wilson, 46, gave up a plumbing business three months ago to lectur at Plymouth College.

He took a pay drop but was attracted by benefits including secure employment and better pension. He said: “I could be earning more out there at the moment but the plumbing trade has its ups and downs. I am at the age when I have to start planning for retirement, and I decided that, in the long-run, it would be better to go for a steady monthly income and a pension.

“Also, as I get older, I don’t want to spend every day doing a job where I am down on my knees.

“You can earn a very good living in plumbing, especially if you start employing people and expanding. But dealing with staffing issues and taxes can be a nightmare. You end up working six or seven days a week. I want time with my family.

“Having said that, the lecturing work is not easy. With the massive demand for plumbing courses, we have trouble recruiting staff we need and that means we all have to take on extra work. But I’ve no regrets about going into lecturing. It’s a very satisfying job.”