Rishi Sunak. File

The prime minister was targeted by social media pranksters who published a video online of the phone ringing before Sunak’s answerphone message kicked in, The Sun reported.

The PM was given a new number when he came to power a year ago, but the pranksters’ video appears to show his personal number still in operation.

The video, also seen by The Independent, shows a phone dialling Sunak’s number. An automated voicemail says “voicemail service for,” before the PM states his name.

It is not known how the number was leaked, and Downing Street said it would not comment on security matters.

A Tory MP on the home affairs committee said he was “sure it is very inconvenient for him,” but was not convinced there was a security breach. “But I'm not sure it constitutes a security breach when thousands of work colleagues & friends probably had it already – as well as hostile intelligence agencies,” the MP said.

It comes two years after it emerged Boris Johnson’s phone number had been online for 15 years, having featured at the bottom of a press release.

At the time, former UK National Security Adviser Lord Ricketts said it was in Johnson’s “own interest to be much more digitally secure than seems to be the case now”.

“I’m talking really of the most senior politicians in sensitive positions, whose phone conversations might well include sensitive material, commercially sensitive material, people trying to lobby them for favours, or tax advantages, or talks with foreign leaders,” he told the BBC.

“And there, I think you do have to accept, just as you do – you can’t just walk around on your own and talk to anyone you like – equally you shouldn’t be in a position where anyone who once had your phone number can get to you when you are a prime minister.

“And that’s one of the inconveniences of being prime minister but it’s for their own sake and their own protection really, that access to them ought to be controlled and monitored.”

Last month Sunak said he could not hand over some WhatsApp messages to the Covid inquiry, which is investigating the government’s handling of the pandemic, because he had changed phones several times and not backed them up.

The revelation about his long-time phone number, which he used while chancellor and during last summer’s leadership election, raised questions about the claim.

The Independent