The UK’s electoral watchdog is seeking to give itself more powers of investigation, which could be in place in time for a potential second Brexit referendum.

The Electoral Commission is proposing to take responsibility for some prosecutions against political parties and campaign groups itself, rather than passing cases to the police.

Pro-Leave politicians and campaigners have expressed concern about the plans, citing fears over alleged bias in the commission against Brexit.

Tory MP Jacob Rees-Mogg told The Sunday Telegraph the Conservative party should formally oppose the move.

“The Electoral Commission is not trusted to be impartial, and a number of its leading figures have said very prejudicial things about Brexit,” he said.

“An independent prosecutor is a safeguard and that’s the whole purpose of a prosecutor. Investigators have a prejudice in favour of prosecuting.”

The election watchdog is to publicly consult on the issue, but said it would be able to extend its remit itself if it decided to.

An Electoral Commission spokesperson said: “This is something that we have been looking at for quite a while.

“We are looking to be able to obtain information. When we talk about obtaining powers of prosecution, we are talking about obtaining information.”

The Electoral Commission insisted the move to gain more powers was not connected to the possibility of another Brexit referendum being held in the next year.

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“We will shortly be consulting with political parties, the police and the CPS on a prosecution policy which will bring our regulatory powers in line with a wide range of public bodies,” the spokesperson said.

“Parties and campaigners are required to comply with our notices should we need information. Where this information is not forthcoming, enhancing our ability to obtain details about how campaigning activities are funded will ensure we can provide voters with transparency.”

Matthew Elliott, who was chief executive of the official Vote Leave campaign, said he believed the commission was not fit for purpose. Last July, Vote Leave was fined £61,000 and referred to the police after an Electoral Commission probe said it broke electoral law.

In September, the High Court ruled that the watchdog had misinterpreted spending rules in its advice to the campaign group, although it agreed Vote Leave had broken the rules.

“The Electoral Commission’s recent bungles have already demonstrated that it is not fit for purpose, so this plot to award themselves the power to prosecute is extremely worrying,” Mr Elliott said.