LONDON — National security concerns were raised following media reports that British Prime Minister Boris Johnson's personal cellphone number has been publicly available on the Internet for the past 15 years.

A contact number listed on a 2006 news release “appears to be the one the PM uses,” the BBC reported Friday, referring to the prime minister.

A spokeswoman for Johnson’s Downing Street office told The Washington Post: “It’s not something we are commenting on.”

Even before the revelation, Johnson faced criticism for “government by text” and how easily he allows himself to be reached by lobbyists or business leaders. In recent days, he has been under scrutiny for texts exchanged with billionaire James Dyson, of vacuum cleaner fame, about special accommodations for employees tasked to make ventilators.

Leaked emails are at the center of a separate controversy about the funding of a lavish refurbishment of the prime minister’s apartment at 11 Downing Street.

Security experts said Friday that if Johnson’s personal number was even more easily accessible than previously thought, he could be at greater risk.

“If his mobile phone number has been that widely available, you can’t rule out that others who you really don’t want to have his number, like hostile states with sophisticated cyber capabilities or criminal gangs, may have it as well,” Peter Ricketts, a former British national security adviser, told the BBC.

“I know that modern systems like WhatsApp are end-to-end encrypted. Nonetheless I think one would be worried if a hostile state, who had sophisticated capabilities, had the mobile phone number itself,” he added.

British politicians are given official work phones, but are allowed to keep their personal phones, as well. And while government ministers have to declare face-to-face meetings with outside groups, they don’t have to declare phone calls, text messages or emails.

Transparency groups say that discrepancy is outdated and has become a problem, especially given the ubiquity of WhatsApp and other messaging platforms in British politics.

Tim Durrant, associate director of the Institute for Government, an independent think tank, noted that during the pandemic, conversations that would normally happen in the “tea rooms” of Westminster are now happening on WhatsApp and Signal. While some of that is “informal conversations,” the messaging platforms can “also be used for lobbying and decision-making,” he said.

“If it’s a conversation about government business, that needs to be recognized,” he said.

The availability of Johnson’s number was first reported by a British gossip website, under a post titled, “Hoping not to butt-dial Boris.”

The site wrote: “It’s not as though the Prime Minister’s personal phone number could just be floating out there on the internet, is it? It would be absolutely insane if it was tacked on to the bottom of an old press release that he dished out freely while MP for Henley, and Shadow Minister for Higher Education.”

The episode was in some ways reminiscent of when a Dutch hacker accessed President Donald Trump’s Twitter account by guessing the password: maga2020!

Some on social media said they were surprised how easy it was to Google Johnson’s number. “Blimey. Took me literally 20 seconds to find it,” wrote one Twitter user.

British Prime Minister Boris Johnson was grilled on April 28 by the opposition over the funding used to refurbish his Downing Street apartment. (PARLIAMENTARY RECORDING UNIT)

Rachel Hopkins, a Labour Party lawmaker who raised concerns at a Parliamentary committee earlier this week about Johnson accessibility, tweeted that Johnson’s continued use of a personal phone had “obvious security & lobbying implications, but also risk of blackmail.”

In 2006, Johnson was a member of Parliament and the Conservative Party’s point person for higher education. He went on to serve two terms as mayor of London before returning to Westminster.

When a Washington Post reporter called the number on Friday morning, it appeared to be disconnected.