Britain’s democracy is one of the most secure in the world and will remain so, a spokesman for Prime Minister Theresa May said on Monday in response to a question about a suggestion that there may have been foreign interference in the Brexit vote.

Opposition lawmaker Ben Bradshaw last week urged the government to look into reports by an advocacy group suggesting that the origin of some Brexit campaign funds was unclear.

Bradshaw said in parliament the issue should be investigated “given the widespread concern over foreign and particularly Russian interference in Western democracies.”

At a regular briefing with reporters, May’s spokesman was asked if the prime minister was concerned about the reports. “I am not aware of those concerns,” he said.

“More broadly, as we’ve always said, the UK democratic system is amongst one of the most secure in the world and will continue to be so.”

The Electoral Commission, which regulates political finance in Britain, said in April it was investigating campaign spending by pro-Brexit organization Leave.EU, without giving details.

A spokeswoman for the Electoral Commission said on Monday that investigation was still going on and it would not provide any further information until it was complete.