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An investigation into whether the official Leave campaign in the EU Referendum broke electoral rules is scheduled to be published within weeks.

The draft Electoral Commission's report concludes that Vote Leave and another smaller campaign group did break the rules, the BBC understands, and is expected to recommend at least one fine.

The latest investigation comes after allegations were made by the whistleblowers Christopher Wylie and Shahmir Sanni that the official Brexit campaign broke the law by colluding with a smaller group, BeLeave.

It is understood that the commission did consider this new evidence, but it is not thought that the new information was decisive in proving a breach of the law.

This is the first full formal investigation into Vote Leave, although the Electoral Commission had twice examined the campaign's behaviour.

One source said that the draft report was "bizarre" and had "gone way off track" by focusing on the original information that has already been pored over, rather than additional evidence.

It's suggested that the commission did not interview, nor request interviews, with the senior members of the Vote Leave Campaign team.

Lawyers for those criticised in the report are understood to be challenging the draft findings, and publication could therefore be subject to delay.

It is not clear if the commission plans only to recommend civil sanctions like fines, or also suggest referring the matter to the police or Crown Prosecution Service.

Suggestions that the official Leave campaign, which featured senior Cabinet ministers, broke the law, would be highly controversial.

Vote Leave and BeLeave have both always denied the allegations.

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An Electoral Commission spokesperson said: "In accordance with its Enforcement Policy, the Electoral Commission has written to Vote Leave, Mr Darren Grimes and Veterans for Britain to advise each campaigner of the outcome of the investigation announced on 20 November 2017.

"The campaigners have 28 days to make representations before final decisions are taken.

"The commission will announce the outcome of the investigation and publish an investigation report once this final decision has been taken."

Lawyer Tamsin Allen, who acts for Mr Sanni, Mr Wylie and a third whistleblower, said "The legal opinion and evidence submitted to the EC demonstrated the grounds for suspecting that Vote Leave and BeLeave conducted an unlawful spending scheme.

"If the Electoral Commission has indeed found those in the scheme guilty of electoral offences, this is vindication for the whistleblowers, but a serious blow for the public and for the integrity of the referendum vote."