Boris Johnson's mobile phone number was freely available for anyone to access on the internet for the last 15 years, according to reports.
A contact number for the Prime Minister was listed on the bottom of a press release when he was still shadow higher education minister in 2006.
That document was still available online in 2021, after some 15 years.
Reports earlier this month suggested senior officials had called on Mr Johnson to change his number because of concerns about how many people contacted him directly.
Downing Street declined to comment on the report - first revealed on the Popbitch gossip newsletter - that Mr Johnson's phone number was available online to anyone who searched for it.
The press release, which related to his work as shadow higher education minister, invited journalists to contact Mr Johnson directly on either a Commons office number or his mobile.
Attempts to call the number on Thursday night were met with an automated message saying the phone was "switched off" and an invitation to "please try later or send a text".
The Prime Minister's use of his mobile phone has been in the spotlight recently after text message exchanges with entrepreneur Sir James Dyson and Saudi Crown Prince Mohammed Bin Salman were leaked.
Earlier this month, The Daily Telegraph reported that Simon Case, the head of the civil service, suggested to the Prime Minister that he change numbers because his current one is too widely known.
