What’s the right price for a good plumber? That’s a tricky question for many people, as prices quoted for disconnecting an old dishwasher and installing a new one ranged from £10 in the Midlands to £90 in south-east England, according to a Which? survey.

In May 2005, posing as ordinary consumers, Which? researchers contacted 240 plumbers across the UK. The plumbers were asked to quote a price for swapping a new dishwasher for an old one. Which? also asked how long the job would take, their hourly rate, and whether they belonged to a trade association (which was then checked).

Not all plumbers give hourly rates; some prefer to give a specific quote for the job. One plumber told Which? that those who charge by the hour tend to "disappear for half an hour to read the paper." Hourly rates discovered by Which? ranged from £9 in Wales to £130 in the South-East.

Call-out charges are another potential hazard. One Romford plumber boasted he charged just £30 per hour. Only later did he admit that he charged a £40 call-out fee.

Many plumbers charge more for the first hour (effectively a call-out charge). Which? found one Cardiff plumber who charged the first hour at five times the subsequent hourly rate. He claimed to charge just £9 an hour — yet wanted £50 for a one-hour job.

The problem is exacerbated by a shortage of plumbers. "An industry where demand outstrips supply leaves open a gap for the cowboys to thrive", said The Institute of Plumbing and Heating Engineering (IPHE) — the main trade body. The Construction Industry Training Board calculates almost 32,000 more plumbers are needed in the UK by 2008 to meet demand.

Which? researchers found the typical rate for plumbers is £30-50 for the first hour, £25-40 for subsequent hours. The consumer organisation also estimates how long common plumbing jobs should take so consumers can work out if a reasonable price is being offered.

Malcolm Coles, editor, Which?, says: "There is a lack of reliable pricing information for plumbers so some get away with daylight robbery. We've carried out a nationwide survey to show how much you should pay. It's time people stopped throwing their money down the drain."