The Plumbers Tax Safe Plan (PTSP) is designed for people working within the plumbing industry who have not told HM Revenue & Customs (HMRC) about all their income in the past and who now want to get back on track. It is intended to cover people who work (or worked) in the plumbing, heating or gas installation trades and this includes anyone who installs and repairs pipes and fixtures for water, drainage or gas systems in a building.
It's basically a 'fresh start'. If you decide to take advantage of PTSP, you can stop worrying about what might have happened had HMRC found out that you'd not been telling them about all of your income. It's a chance to start getting things right from now on, whilst knowing exactly how much it's going to cost to sort out things for the past.