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LONDON (Reuters) - Britain’s ruling Conservative Party has been fined 70,000 pounds ($85,932) for breaching rules which govern spending during an election campaign and the matter has been referred to police, Britain’s Electoral Commission said on Thursday.

The fine, the largest of its kind, was imposed on Prime Minister Theresa May’s party after the commission found “significant failures” to report accurately how much it spent on campaigning at three by-elections in 2014, and at the 2015 UK national election.

Some returns were incomplete or inaccurate and did not conform to rules governing spending on campaigning at a local and at a national level. The commission said it had referred one incident to London’s Metropolitan Police Service.

The news comes at a sensitive time for May who is about to start the formal process for taking Britain out of the European Union.

“Our investigation uncovered numerous failures by a large, well-resourced and experienced party to ensure that accurate records of spending were maintained and that all of the party’s spending was reported correctly,” John Holmes, chair of the Electoral Commission, said in a statement.

“Where the rules are not followed, it undermines voters’ confidence in our democratic processes, which is why political parties need to take their responsibilities under the legislation seriously,” he said.

Britain has spending limits in local campaigns which are different to those on national campaigns to ensure fair play.

The Conservatives said in a statement it was the first time the party had been fined for a reporting error.

“We regret that and will continue to keep our internal processes under review to ensure this does not happen again,” the party said.