LONDON — The British government downplayed allegations Friday of a security risk after it was reported that Prime Minister Boris Johnson’s cell phone number was openly available on the internet for 15 years.

Celebrity website Popbitch revealed that the number was on a think tank press release from 2006, when Johnson was an opposition lawmaker and the Conservative Party’s higher education spokesman.

Callers to the number on Thursday night heard an automated message saying the phone was “switched off.” By Friday it appeared to no longer be in use.

Home Office minister Victoria Atkins insisted that the prime minister “knows his responsibilities when it comes to national security,” and criticized media for revealing the fact that the number was in the public domain.

But former National Security Adviser Peter Ricketts said 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.”

Johnson is already facing questions about his text and WhatsApp message exchanges with business leaders and lobbyists.

He has denied doing anything wrong when he exchanged text messages last year with industrialist James Dyson and promised he would “fix” the tax rules for him if Dyson agreed to make ventilators for the National Health Service.