London: Australia, the US and the rest of the Five Eyes countries should be "extremely concerned" about Prime Minister Boris Johnson's chief of staff accessing its top-secret intelligence, a British MP has warned.

Dominic Cummings' security clearance has come under scrutiny in the British press, following reports he had been "developed vetted", or given the highest security status, enabling him access to the highest levels of intelligence.

Boris Johnson's special adviser and former Leave campaigner Dominic Cummings arrives at 10 Downing St. Credit:AP

But it was also reported that officials have been withholding classified material from Cummings because of the time he spent in Russia during his 20s, when he is alleged to have cultivated relationships with prominent backers of Russian President Vladmir Putin.

Downing Street said it did not comment on the security clearance of individuals.