Sir Keir Starmer's chief of staff has been accused of hiding a £50,000 donation after being told to declare his funding.
Morgan McSweeney's think-tank Labour Together reportedly received the cash on the same day the Electoral Commission confirmed he was required to declare all donations exceeding £7,500 within 30 days.
Despite this, the payment was kept secret for three years, by which time Mr McSweeney was working as the Labour leader’s spin doctor.
The news raises questions about Labour Together's suggestion this week that its failure to report more than £700,000 in gifts was due to “human error and administrative oversight”.
It also adds pressure on the Commission to reopen an investigation into Labour Together, which was fined £14,000 for more than 20 breaches of election law.
The Conservatives had called for a new probe into the handling of donations during Mr McSweeney's time as Labour Together's director, claiming leaked emails showed he had attempted to cover up the late reporting of donations as an administrative error.
Kevin Hollinrake, the chairman of the Conservative Party, told the Daily Mail: 'This is just the latest staggering revelation about the Morgan McSweeney scandal.
“This scandal strikes right at the heart of Starmer's government. The Conservatives have demanded a full investigation and will continue to fight until the public get the truth.”
However on Friday the Electoral Commission said will not reopen its investigation into undeclared donations.
A spokesperson for the watchdog said it had found "no evidence of any other potential offences".
When approached by the Commission in 2017, Mr McSweeney argued that Labour Together was not involved directly in campaigning for the Labour Party.
But the Commission rejected Mr McSweeney’s argument as Labour Together is considered a “members' association” and had a duty to declare its funding streams.
On December 6, 2017, the day the Commission wrote to Mr McSweeney, Labour Together received a £50,000 donation from investor Martin Taylor.
However, the bank transfer was not made public until 2021, with Mr McSweeney claiming in a leaked email to Labour lawyers in “early 2018” that Labour Together did not have to make any declarations.
Gerald Shamash advised Mr McSweeney it would be better to portray the episode as an “admin error” and “not refer to you at all”.
A spokesman for Labour Together said it “proactively raised concerns” about the need to declare donations and “fully co-operated” with the Electoral Commission.
The Electoral Commission said its investigation “proved beyond reasonable doubt that failures by the association occurred without reasonable excuse”.
