The Commissioner, Kathryn Stone, provides very limited details about MPs under investigation, of whom there are currently two others in addition to Starmer and Lammy: the Home Office minister Chris Philp and a Conservative backbencher, Andrew Bridgen.
Mr Lammy’s alleged late declarations are thought to relate to extra-curricular earnings for speeches around Black History Month last October, which were not declared until May this year.
It is also thought the investigation will look at trips that were made by Mr Lammy, who has been the MP for Tottenham since 2000, to Tottenham Hotspur football club.
Mr Lammy, 49, has been approached for comment.
Mr Lammy was highly critical of Boris Johnson when the Prime Minister was referred to Ms Stone over the redecoration of his Downing Street flat.
In May 2021, he tweeted: “Boris Johnson’s defense appears to be that he had no idea how his £200,000 decoration bill would be paid. If true, how are we expected to trust this bumbling fool to run the UK economy?”
It came after he appeared on his LBC show a month earlier reminding listeners of the importance of the Nolan Principles of Public Life, saying: “(They’re) a really important set of principles which should govern the way I and others should behave in public life: honestly, openness, objectivity, selflessness, integrity, accountability and leadership.
“Of course we care about who funded the refurbishment of the No 10 flat.”
In January 2022, Ms Stone confirmed she would not investigate the refurbishment after he was cleared of breaking the ministerial code by his former standards adviser, Lord Geidt.
However, Mr Johnson was criticized by the peer for not disclosing all the details about the funding.