An energy supplier has launched a probe into the activities of its doorstep sales staff in Keighley.

Npower promised the investigation this week after hearing claims its callers were poaching customers from Yorkshire Electricity.

A YE representative allegedly told a Keighley woman that Npower staff were signing-up householders without their knowledge or consent.

The confusion concerns the new competitive market for energy supply, which allows people to buy their gas or electricity from any company.

Firms such as Npower - formerly National Power - and Powergen send doorstep callers to persuade people to switch from British Gas or Yorkshire Electricity.

The woman, who lives on Parkwood Street, says a sales team - believed to be from Npower - called at her house twice last month.

She says: "Their presence was intimidating. They wouldn't take no for an answer.

"I had to be very forceful with them and shut the door in their faces."

A fortnight later the mother-of-two opened the door to a Yorkshire Electricity representative who was calling at every house in Parkwood Street.

The rep claimed YE had received notification from Npower that several homes in the area wanted to switch their electricity supply.

When YE contacted those customers individually at least four allegedly responded that they had not signed any such agreement. On being told of the allegations, N Power promised a "full and immediate" investigation.

A spokesman says: "We're keen that Npower sales agents act in accordance with the highest standards.

"We take any complaint against our direct sales advisers extremely seriously, and where individuals are found to have acted inappropriately we immediately take relevant action which can include dismissal."

The spokesman says NPower agents operate to strict procedures laid down by the Association of Energy Suppliers' code of conduct.

Customer contracts are clearly marked so householders know they are changing their supplier. Customers have 14 days to cancel and a 28-day "second thoughts" period.

A spokesman for Yorkshire Electricity confirms a representative of its sales team had been out in Parkwood following the Npower visits. She adds: "We can confirm we have had complaints but can't confirm the area. We had some complaints in the Hull area about Npower. I think they're doing aggressive sales."

Yorkshire Electricity occasionally visits customers who have switched companies in an attempt to win them back.

Graham Hebblethwaite, from West Yorkshire Trading Standards, says his officers have not received any complaints specifically about Npower. But he says that in the past numerous people have complained about the selling techniques of various firms.

He adds: "There were some people offering exaggerated savings or asking for some sort of joining fee. There certainly is great rivalry."

Anyone who wants to complain about energy firm s should contact the Office of Gas and Electricity (OFGEM) on 0800 887777 or at Symons House, Belgrave Street, Leeds, LS2 8DD.