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Labour have raised "serious" security concerns about the Russian past of one of the Prime Minister's top aides.

Durham-born former Vote Leave director Dominic Cummings is a senior advisor to PM Boris Johnson.

But opposition politicians have highlighted unverified claims he could have formed links with individuals involved in "politics, intelligence and security" in Russia, when he worked there in the 1990s.

Shadow foreign secretary Emily Thornberry wrote to her Tory counterpart Dominic Raab to ask if Mr Cummings has been granted access to the Government's most sensitive "top secret" intelligence files.

In a letter copied to the heads of MI5 and MI6 and Cabinet Secretary Sir Mark Sedwill on Friday, she said Labour did not "know the veracity of their claims" but felt compelled to inform officials of them.

She wrote: "I am writing to you based on the serious concerns that have been raised with shadow ministers by an official-level whistleblower," she wrote.

"I feel duty-bound to put to you the concerns raised with the Labour front bench by a whistleblower whose motives we have no cause to question."

The individual was said to have approached Labour figures to question "relationships" Mr Cummings may have fostered during his time in Russia.

Mr Cummings is yet to respond to a request for comment on the letter, which was first reported by the Sunday Times.

(Image: Getty Images)

The Cabinet Office said: "We do not comment on individuals' security clearance."

The advisor was born and raised in Durham, and cut his teeth in politics during the the 2004 local referendum campaign on regional devolution, where he spearheaded a successful 'No' campaign, and campaigned against Britain joining the Euro in 1999.

On his blog, Mr Cummings briefly mentions his Russian experience, saying: "I worked in Russia 1994-7 on various projects".

The questions came as the Prime Minister faces calls to publish a key report assessing the threat posed by Russia to Britain's democratic processes.

Former attorney general Dominic Grieve, who has seen the dossier, stressed must be published before of the General Election, as it contains information "germane" to voters.

Liberal Democrat leader Jo Swinson also called on the Government to stop "keeping it a secret".

Mr Grieve, chairman of the Intelligence and Security Committee at Parliament, has accused the PM of sitting on the report ahead of the December 12 vote.

The independent MP, who was exiled from the Tories by the PM over his no-deal Brexit opposition, is calling on the Conservative leader to publish the committee's report before Parliament is dissolved on Tuesday.

A Downing Street spokeswoman said: "There are a number of administrative stages/processes which reports such as this - which often contain sensitive information - have to go through before they are published.

"This usually takes several weeks to complete. The committee is well informed of this process."