Gordon Brown calls for change to rules as he and other ex-leaders say they do not use allowance for commercial work

Three former prime ministers have said they do not use a taxpayer subsidy for their private office for any commercial work after the Guardian revealed Boris Johnson appears have done so.

One of them, Gordon Brown, said that rules should now be changed to require former prime ministers to publicly declare their business interests. He said there should be a crackdown on the jobs taken by former ministers.

Brown, Tony Blair and Liz Truss all said they had only claimed for reimbursements related solely to their public duties.

There are mounting questions over whether Johnson has been misusing his portion of the £5.2m in public funds that has been paid out since 2015 as part of a scheme to support former prime ministers.