The Kremlin has long sought to weaken or divide the European Union, perceiving it as a rival for influence in countries from the former Soviet bloc. And Russia’s main propaganda outlets like Sputnik and Russia Today pushed hard for Brexit.

But the British government, consumed by the negotiations for an exit from the European Union, has not yet obtained similar disclosures. Although a parliamentary committee recently asked the social media companies for information, many critics have argued that the government has little appetite for an inquiry that could muddy its mandate.

The social media companies, including Facebook, Twitter and Google, have had little incentive to volunteer information about the exploitation of their own platforms. And the predominantly right-wing, pro-Brexit British press, particularly the powerful tabloids, have little enthusiasm for undermining the validity of the referendum.

That dynamic may now be changing. The Times of London reported on Wednesday that a team of researchers working on an unrelated and still-unpublished study had identified 156,252 Twitter accounts that listed Russian as their language but posted messages in English to argue against the European Union.

The researchers, Oleksandr Talavera and Tho Pham, of Swansea University in Wales, said in interviews on Wednesday that the Russian accounts, which had posted very little about Brexit in the month before the referendum, became quite active at the last minute: from about 1,000 a day two weeks before the vote to 45,000 in the last 48 hours and 39,000 on the day the results were announced, June 24, 2016.

“It is very strange that someone whose language is Russian tweets in English,” Ms. Pham said — describing it as an anomaly that had prompted the researchers to look more closely at 10 of the most active accounts under suspicion.

Nine had been deleted, and the last, Sveta1972, appeared to emanate from a Russian resort town. On the eve of the referendum, Sveta1972 urged Britain to “make June the 23rd our Independence Day.”