Matt Peacock at Ofcom, the telephone regulator, said: “The level of competition in the home-phone market gives consumers a very powerful tool — choice — and they need to use it. It is not illegal for someone in a sales position to be pushy but it can be very annoying. If a salesperson has angered you in this way, you should ring the company and say that its sales practice is counter-productive.

“The best way to punish bad sales tactics is by saying no, and taking your business elsewhere.”

Cold calling and door-to-door selling appear to be a big problem at the moment. About 18m households are being plagued by telephone sales calls and 8m targeted by door-to-door salespeople, according to a survey conducted by market- research group Chat About Money for Uswitch.com, a price-comparison service.

And this type of selling seems to be rife in the home-phone market. BT said it received about 21,000 complaints a month from customers saying that a rival company had contacted them either pretending to be from BT, or trying to get them to switch providers.

BT said: “Competition is great because consumers get better deals, but what is completely unacceptable are the underhand sales tactics now running at epidemic levels.”

Some firms do appear to be breaching regulations. Ofcom is investigating a number of providers thought to be in breach of its code of practice. These include Platinum Telecom UK, Lo-Rate Telecom and Just Telecoms. The main problems are slamming and mis-selling.

Slamming is when your home phone is switched to a different provider without your consent. Ofcom said the worst case of slamming it had heard about involved a telesales person who pretended to be from BT and rang a customer asking them to confirm their account and personal details. These were then used to transfer them to another phone provider.

Another, more common, tactic is for a phone company to ring you at home and say you could save money by switching to them. They then ask if you would like more information: if you say yes, that is taken as the green light for them to switch you over.

Often the first consumers know about it is when they receive a letter from their new provider informing them of the date their service will be switched.

If you were put under pressure to transfer your service, given misleading information or had to buy the service just to get information about it, you may have been a victim of mis-selling.

Peacock said: “If you have been slammed or think you have been mis-sold tell Ofcom as we need to know about it.”

You can register your complaint at ofcom.org.uk. You can also reduce the number of unsolicited sales calls you receive by registering with the telephone preference service. Call 020 7291 3320, or sign up at tpsonline.org.uk.

For more on consumer affairs visit www.timesonline.co.uk/consumeraffairs