LONDON — Britain’s Electoral Commission is investigating whether a major backer of the campaign to leave the European Union broke campaign finance laws.

The commission says it is probing whether businessman Arron Banks, chairman of the group Leave.EU, committed offenses over campaign donations or loans.

The investigation focuses on Better for the Country Limited, a company which lists Banks as a director. It was not registered as a participant in the 2016 referendum, but five registered campaigners reported donations from it totaling more than 2.3 million pounds ($3 million).

Labour Party lawmaker Ben Bradshaw has urged the government and electoral officials to investigate reports of “the role of dark money” in the referendum campaign.

Banks denied wrongdoing Wednesday and accused the establishment of “trying to discredit the result” of the referendum.