A UK national security adviser has said Boris Johnson should be much more digitally secure after reports that the prime minister’s mobile phone number has been available online for the past 15 years. Peter Ricketts said Johnson’s phone conversations may well include “sensitive material” and “people trying to lobby them for favours, or tax advantages, or talks with foreign leaders”. Asked if there could be security concerns, he told BBC Radio 4’s Today programme that if the number had been widely available, it could not be ruled out that hostile states or criminal gangs could have access to it. “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 said. “That must increase the risk that they are able to eavesdrop on some at least of the communications that are going on, and possibly other non-state actors as well, like sophisticated criminal gangs. So, there is no way of knowing whether that’s true, but there must at least be an increased risk if the number is widely available. “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,” he told BBC Radio 4’s Today programme. A contact number for Johnson was listed on the bottom of a press release when he was still shadow higher education minister in 2006 – a document that was still available online in 2021. Reports this month suggested senior officials had advised Johnson to change his number because of concerns about how many people contacted him directly. Downing Street declined to comment on the report, revealed on the Popbitch website, that Johnson’s phone number was available online to anyone who searched for it. The press release, which related to his work as a shadow minister, invited journalists to contact Johnson directly on either a Commons office number or his mobile. The Home Office minister said Johnson was aware of his responsibilities on national security. “The prime minister, more than anyone, knows his responsibilities when it comes to national security,” Victoria Atkins told Times Radio Breakfast. “I’m slightly surprised that a national broadcaster felt it appropriate to advertise the fact that that mobile phone is on the internet if indeed it is.” She added that she believed the public was not “particularly interested” in the issue. Lord Ricketts said it was for Johnson’s interest that his number should be protected, and it was “one of the inconveniences of being a prime minister”. Johnson’s use of his mobile phone has been in the spotlight after text message exchanges with the entrepreneur Sir James Dyson and Saudi crown Prince Mohammed bin Salman were leaked. Ricketts said: “So that there can be no suspicion of favours asked for and done or the kind of things that we are now seeing with the exchanges that we see with James Dyson. I think it’s for the prime minister’s own interest to be much more digitally secure than seems to be the case now.” This month, No 10 refused to deny reports that Simon Case, the head of the civil service, suggested to the prime minister that he change numbers because his current one was too widely known. 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”.