HMRC is contacting around 50,000 plumbers, heating engineers and gas fitters to give them the opportunity to come clean about any unpaid taxes.

A letter being sent out will explain that, once the opportunity expires, HMRC will begin a clampdown on those working in the sector who have failed to declare earnings and pay the tax they owe.

Plumbers, gas fitters, heating engineers and members of associated trades who owe tax which they have not yet declared can come forward anytime up to 31st May to tell HMRC they want to take part.

If they make a full disclosure, most face a low penalty rate of 10% to 20%. Once they come forward, they have until 31st August to make their disclosure and arrange for payment.

After that date the tax office will investigate those that have not come forward.