Downing Street says Boris Johnson's chief adviser "regularly visits Government sites", following reports Dominic Cummings is due to visit classified military areas.
The Sydney Morning Herald claims to have seen private correspondence between those involved in planning the visits, with Mr Cummings expected to look at five locations including Porton Down in Salisbury, which is home to the Defence Science and Technology Laboratory, and the SAS headquarters in Hereford.
On Tuesday, Conservative MP Mark Francois warned General Sir Nick Carter Dominic Cummings "will sort you out his own way".
A Number 10 spokesperson told Forces News: "Mr Cummings, he is, of course, the Prime Minister’s senior adviser, so being in that position he regularly visits government sites and meets ministers.
"Similar visits have taken place involving senior advisers under previous governments."
Liberal Democrat MP Layla Moran said those who care about the Armed Forces should be "deeply worried" by reports of the "unprecedented" visits.
"Everyone who cares about our armed forces should be deeply worried by these developments. Britain’s defence should not be the political plaything of Dominic Cummings."
The Government’s integrated review was launched in February and has been described as the deepest review of British foreign, defence and security policy in 30 years.