A Labour lawyer advised Morgan McSweeney, Sir Keir Starmer’s chief of staff, that a failure to disclose £700,000 of donations should be marked as an “admin error”, a leaked document has revealed.

The document from 2021 was published by the Conservatives on Tuesday. In the email, Gerald Shamash, the Labour lawyer, said that there is “no easy way” to explain the failure to disclose the donations, especially as the elections watchdog had advised that they needed to be reported.

Shamash laid out a series of questions to McSweeney, 48, about the donations, with the addendum that if they can not be answered, then it is “perhaps best” to put it down to an “admin error”.

In a leaked email from 2021, Gerald Shamash, the Labour Party lawyer, told McSweeney there was “no easy way” to explain the failure to disclose the donations

The Labour Together think tank, of which McSweeney was the director and company secretary from 2017-20, was fined £14,250 for more than 20 breaches of electoral law in 2021 but the publication of the new document has reignited a row. Kevin Hollinrake, the Tory chairman, said: “Morgan McSweeney has been caught red-handed hiding hundreds of thousands of pounds which helped install Keir Starmer as Labour leader. This latest scandal at the very heart of government is incredibly serious”.