Ofcom has amended its rules regarding 070 and 030 telephone numbers.

From September, callers to numbers which start with the digits 070 must be issued with a free warning if the call will cost more than 20p before being connected, the telecoms watchdog has said.

Numbers beginning 070, known as “follow me numbers”, are used by companies that are not based in an office, for example plumbers, as they divert the caller straight to a mobile or other number chosen. They are also often used to create anonymity when selling items.

Such numbers can be bought from websites by anyone for as little as £250. Companies can then charge up to £2 for a 10 or 15 second call. Many people are often caught out by these because 070 usually symbolises a mobile number.

Ofcom has been fighting to change the way these numbers work since July 2006 because it believes that there has been a “lack of transparency” surrounding them. It also plans to remove personal numbering services from 070 numbers and replace them with 06 to distinguish them clearly from mobile phone numbers.

An Ofcom spokeswoman told Computeractive that “the new rules will aim to make clear what is and what is not a premium number”.

"People in the past have been confused when calling such numbers because they look so similar to a mobile number. We hope by changing the regulations and adding the verbal warnings that people will be less likely to fall victim to high call costs.” she added.

Premium rate services regulator ICSTIS welcomed the move by Ofcom. Spokeswoman Kate Belson said: “Whilst we only deal with 070 numbers if they are being used for a premium rate style services, we welcome anything that will give more clarity to the consumers.”

In addition Ofcom has also introduced 030 numbers as an alternative to chargeable 08 numbers, for example 0870, which it “expects all businesses to take up”.

The first 03 numbers, which are likely to be in use for the public to call later this year, will, according to Ofcom’s spokeswoman, “cost no more than calls to geographic numbers (those starting with 01 or 02)”.

“The 03 calls will be included as part of any inclusive minutes or discount schemes [on mobiles or landlines] in the same way as geographic calls,” she said.