Chris Gow, who lives in Obelisk Rise, Kingsthorpe, said he had been getting late-night calls since the numbers changed two months ago.

Mr Gow's phone number has begun with the digits 844 for the past 30 years, but said when he complained about the problem it was suggested he got a new number.

He said: "I get dozens of people phoning me trying to get their doctor. It's bad enough they get charged extra to call their doctor but when they call me by mistake they have to pay for that call again."

The new numbers cost 5p to call from a BT landline and more from mobile networks, but GP practices – including Abington Health Centre, Delapre Medical Centre and Danetre Medical Practice – said they helped them handle calls more efficiently.

Mark Leonard, manager of Delapre Medical Centre, said the new system was only possible using 0844 numbers.

"We do a patient survey and the surgery scored low for accessibility because of the old telephone system.

"Since the new one has come in, that score has gone up by about 40 per cent."