UK Prime Minister Boris Johnson has had the same mobile phone number for 15 years and it has been freely available since it was published in a press release in 2006, several UK media reports claimed on Friday.

While Downing Street has declined to comment, some media outlets tried dialling the number in question but it appeared to be switched off. The Opposition Labour Party has said the easy availability of the UK Prime Minister's number had implications for security, lobbying and the risk of blackmail.

The think tank press release in question was related to Johnson's then-job as a shadow higher education minister and member of Parliament for Henley. It invited journalists to contact him for further comment. Two years later, Johnson went on to become the Mayor of London.

The number's availability was first reported by a weekly UK-based celebrity gossip newsletter ‘Popbitch'.

It comes as questions have been raised in recent weeks over who has access to ministers' personal phone numbers, amid a wider row about lobbying and influence.

It escalated further as text messages between Johnson and vacuum cleaner entrepreneur James Dyson were leaked and purported to show a discussion over tax rules.

He has denied any wrongdoing, and said the exchange was to secure ventilators for the National Health Service (NHS) at the peak of the COVID-19 pandemic last year.

‘The Daily Telegraph' reported earlier in April that Simon Case, the head of the civil service, said the UK prime minister should change phone numbers because his was too widely known.

Last week, 10 Downing Street had denied the prime minister had been advised by senior officials to change his number.

Former National Security Adviser Peter Ricketts warned that if the number was widely available it could be used for eavesdropping by hostile states, “and possibly other non-state actors as well, like sophisticated criminal gangs”.