LONDON — The British government came under heightened pressure to disclose details about a secretive scientific advisory group after a report on Friday that a top political aide to Prime Minister Boris Johnson had taken part in the group’s meetings on the coronavirus pandemic.

The adviser, Dominic Cummings, as well as a data scientist with close ties to Mr. Cummings, attended a meeting of the Scientific Advisory Group on Emergencies, or SAGE, on March 23, the day Mr. Johnson ordered a lockdown to try to curb the spread of the virus, according to a report in The Guardian.

Mr. Cummings was a major strategist in the 2016 campaign for Brexit and is viewed as one of the masterminds of Mr. Johnson’s landslide election victory in December, when he used the slogan “Get Brexit Done.” The data scientist, Ben Warner, worked with Mr. Cummings on the Brexit “Vote Leave” campaign.

The government has refused to disclose the members of SAGE or publish the minutes of its meetings, citing the security and independence of the scientists. That has raised questions about its role, particularly after the government abruptly shifted its response to the virus in late March from a more relaxed approach to a lockdown that put Britain in line with other European countries.