Sir Keir Starmer has been advised to change his mobile number as he has been getting "too much unsolicited advice".
A senior Labour official told The Sunday Times that "people are popping up from 20 years ago telling him what they think".
Sir Keir is understood to receive counsel from Tony Blair and Gordon Brown, though officials said the former prime ministers would be given the current Labour leader's new mobile number if he were to change it.
Mr Blair, an official is cited as saying, "tends to push very Blairite issues like technology and modernity", while Mr Brown "wants to be involved in big projects".
The former PM has also given advice to Rishi Sunak, a Tory source told the paper. At events marking the 25th anniversary of the Good Friday Agreement, the prime minister was seen speaking to Mr Blair.
"They had a nice chat and compared notes on prime minister's questions," the source said. Asked if the chat extended to giving advice, they said: "There was a bit of that, yes."
At Wednesday's Prime Minister's Questions, Mr Sunak used a quote from Mr Blair against the serving opposition leader, saying: "The right honourable gentleman can be as cocky as he likes about the local elections; come a general election, policy counts."
Si Keir aides told the paper that Sir Keir seeks the advice of Mr Brown frequently.
Last December, Mr Brown unveiled a mammoth set of proposals for changing Britain's constitution to give more power to English regions and revise the devolution settlements for Scotland, Wales and Northern Ireland.
He was working on commission from Sir Keir, though the Labour leader stopped short of endorsing the reform package.
One aide is cited as saying the process was "classic Gordon", adding: "We would be on the Zoom calls with him and people would say, 'This bit has to go,' and Gordon would say, 'Yes, yes,' and when the paper came back it was 50 pages longer."
On Friday, Sir Keir echoed Mr Blair by dubbing a plan to reform Labour as Clause 4 "on steroids", a reference to the former prime minister's pivotal fight with his party to ditch a commitment to public ownership of industry.
British politics has a long tradition of former prime ministers making their views known to the party leaders who follow them - and not always behind closed doors.
Margaret Thatcher was something of a thorn in John Major's side. Having announced her intention on stepping down as prime minister to be "a backseat driver", she went on to share her advice in public, criticising her successor's key Europe policy.
Mr Sunak is reported to have frequent private conversations with Theresa May, though this has not stopped her from airing her opposition to his policies, including the government's controversial plans to tackle small boat crossings.
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