The 20,000 fake phone numbers

It is nearly 15 years since UK phone numbers were given a shake-up. Some 20,000 numbers were kept unused, except for appearances on television screens. Why are so many required, asks Chris Stokel-Walker.

Ask a Doctor Who fan to identify the phone number 07700 900461 and they'll say in a flash it's the direct line to the Doctor, as mentioned in a 2008 episode of the television programme. But ring the number, and an automated voice says it's not recognised.

The number is one of 20,000 kept aside by Ofcom, the telecoms regulator, for use in television and radio drama and films following the Big Number change on 22 April 2000, which freed up more capacity on the network. Of these numbers, some 15,000 are geographical ones, often based around large cities or regions, including Leeds, London, Bristol, Tyneside and Northern Ireland. A further 4,000 numbers are held back from everyday use to stand in for mobile numbers (07700), freephone calls (08081), premium rate services (0909) and UK-wide telephones (03069).

"For viewers, it's all about realism," says Ofcom's Joe Smithies. "The idea is to present a number they recognise as being relevant to the context of the story. That could be a local area number, an 0161 number for Coronation Street, or 020 for Eastenders, or 07 for a mobile number."

Another 1,000 UK numbers are set aside in a fictional geographic area with the dialling code 01632, for those series or films that don't want to peg themselves to a certain area, or are set outside those covered by Ofcom's reserved numbers database. In the United States, 555 has traditionally been used for television programmes and films, though some 555 phone numbers are active connections.

There is another reason that Ofcom takes the time and effort to keep numbers inactive just for television programmes. "If you use a number used by someone else, that person or party could quite rightly be annoyed because they get calls from eagle-eyed viewers," explains Smithies. Just ask any American residents whose telephone number includes 867-5309, the name of a 1981 song by Tommy Tutone, many of whom field prank calls each day.

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