Plumbing carries no licence, so the word on the side of the van tells you nothing about competence. One part of the trade is different, and it is the part to check first.
Gas is the only hard legal line
Under regulation 3 of the Gas Safety (Installation and Use) Regulations 1998, nobody may carry out work on gas fittings or appliances unless they belong to a class of persons approved by the Health and Safety Executive, which in practice means the Gas Safe Register. Working outside it is a criminal offence rather than a lapse in best practice.
Being a plumber does not make somebody Gas Safe registered, and the answer on what questions to ask a plumber sets out why, and how to check. The red flag here is narrow and decisive: anyone who agrees to touch a boiler, a gas hob or a gas fire without offering a registration number you can check at gassaferegister.co.uk.
Every other credential in this trade is voluntary, including WaterSafe, CIPHE, APHC and TrustMark. They carry real information, but their absence breaks no law.
What the public record supports
This is where most pages on the subject stop being reliable, so the evidence is worth stating exactly.
There is no adjudicated UK case establishing that plumbers routinely invent faults. There is no verifiable Which? undercover investigation of emergency plumbers, despite that being widely assumed to exist. And a search of Advertising Standards Authority rulings from 2023 to 2026 turned up none against a plumbing firm for overcharging, which is an absence of evidence rather than proof that none exists. Repeating those claims would be doing the thing this page exists to warn you about.
What is documented is narrower and more useful. The ASA ruled in 2020 that advertising "No Call Out Charge" was misleading where a diagnostic visit was still billed, which is an advertising finding rather than a criminal one. At the far end, a fraudulent trading conviction in 2024 carried a three-year prison sentence and a ten-year Criminal Behaviour Order, which shows what the ceiling looks like. Prosecutions on that scale are rare. The ordinary bad outcome is a civil argument about money.
The pattern that costs people money
Almost none of it involves deception. It involves a price that was never fixed.
Section 51 of the Consumer Rights Act 2015 says that where no price was agreed at all, you owe a reasonable price and no more. That sounds like protection until you notice its limit: if you agreed £400, you owe £400, however the afternoon went. The leverage sits entirely before the work starts, which is why the price question is worth asking twice.
The trade separates a quote, meant as a fixed figure, from an estimate, meant as an indication. That is convention rather than statute, since no legislation defines either word, so what matters is whether the number is in writing and what it says it covers.
The red flags that hold up
Which? lists the markers of a rogue trader, and each transfers cleanly to plumbing: an approach you did not initiate, a large deposit or cash demanded before anything has started, vague business details such as a mobile number and no address, no accreditation of any kind, and unwillingness to put a quote, a contract or an invoice in writing.
Deposits deserve a plumbing-specific note. No legal cap exists, and the 25% ceiling in circulation is Citizens Advice guidance, echoed by the FMB. But a plumbing repair is hours rather than weeks, and both bodies frame a legitimate upfront payment as a contribution towards materials. On a tap or a blockage there is usually nothing to fund, so a deposit request on a small repair is worth a question rather than a transfer.
Cold calling is a legal matter too
Doorstep selling of this kind is a banned practice, not merely a bad sign, and the answer on how to spot a dodgy builder sets out the rules and the penalties.
Doorstep plumbing is rarer than doorstep roofing, because a stranger cannot read your pipework from the pavement. Where it happens it tends to follow something visible: a skip outside, a damp patch on a party wall, work going on next door.
Emergency pricing is not evidence of anything
The largest number on most contested plumbing invoices is urgency, and it is legitimate. Checkatrade puts out-of-hours and emergency work at up to twice the normal hourly rate plus a call-out charge, with a same-day call-out at £110 to £180 against around £60 for a booked visit.
Knowing that at eleven at night changes what you do: isolate the water at the stopcock if you safely can, and book for the morning.
Judging a stranger at midnight is the hardest version of this problem, and the cheapest fix is to have chosen someone already.