Boris Johnson has branded claims Vote Leave “cheated” during the Brexit campaign “utterly ludicrous” as demands for answers over spending intensified on Sunday.
The Foreign Secretary tweeted that the designated Leave campaign “won fair and square - and legally” after allegations by whistleblower Shahmir Sanni it used separate pro-Brexit group BeLeave to dodge strict spending limits set by the Electoral Commission.
Vote Leave has strongly denied wrongdoing and said the £625,000 donated to BeLeave was within the rules.
Johnson was not backed by his cabinet colleagues on Sunday, however.
Brexit Secretary David Davis told the BBC’s Andrew Marr Show: “It’s really a matter if there’s any truth in it at all for the Electoral Commission to investigate. That’s for them, not a minister to decide.”
Health Secretary Jeremy Hunt, speaking on ITV’s Peston On Sunday, added: “It has to be something that the Electoral Commission decide.”
A string of Remain-leaning MPs have gone on record to say Vote Leave, and the Government ministers involved in the campaign, have questions to answer.
Johnson, Transport Secretary Chris Grayling and International Development Secretary Penny Mordaunt are among the government ministers who campaigned with Vote Leave.
Deputy Labour leader Tom Watson told Marr: “The leaders of Vote Leave are senior cabinet ministers. We need answers about what really went on.”
Former Cabinet minister and Tory MP Nicky Morgan said allegations the officially-designated Brexit campaign “cheated” on spending were “very concerning”.
“Democracy is a very important and very precious thing,” she told LBC.
“If people start thinking they can go around undermining the law on it, then I think that actually is a really bad step for our democracy.”
Green co-leader Caroline Lucas told Marr on Sunday: “What these revelations demonstrate is that there is something rotten at the heart of our democracy and that we need to be overhauling our rules that govern elections.”
She added: “What I want to see is a real investigation into exactly who knew what - the ministers associated with the Vote Leave campaign, what did they know about the money that was going to BeLeave?
“What was the relationship between Vote Leave and BeLeave and then... what was the relationship between BeLeave and AggregateIQ based in Canada?
“This is a really complex network - but big, big questions need to be asked and it goes much wider than just the referendum”.
Liberal Democrat Brexit spokesman Tom Brake said police should be called in.
“These allegations are stunning and touch directly on one of Theresa May’s closest advisers,” he said, adding: “These allegations must be examined by the police.
“If they represent what happened it is outrageous and shameful.
“The referendum had a very narrow outcome. One of the biggest exercises in democracy must not turn out to be one of Britain’s biggest electoral frauds.”
The allegations centre on Sanni’s claims that BeLeave was controlled by Vote Leave rather than an independent campaign.
Sanni told Channel 4 News: “In effect they used BeLeave to over-spend, and not just by a small amount... Almost two-thirds of a million pounds makes all the difference and it wasn’t legal.”
Senior Vote Leave figure Stephen Parkinson - now Theresa May’s political secretary - said: “At the relevant time during the referendum period, the commission advised Vote Leave that it was permissible to make a donation in the way it proposed to do to BeLeave.
“Twice since the referendum the commission has investigated this matter, and twice it has found no evidence of wrongdoing. A third investigation into the same issue is currently taking place.
“The Electoral Commission has not contacted me in relation to any of these inquiries, but I will of course be happy to assist in them if they wish me to do so.
“I firmly deny the allegations in the programme.
“I had no responsibility for digital campaigning or donations on the Vote Leave campaign, and am confident that I stayed within the law and strict spending rules at all times.”
Darren Grimes, from BeLeave, also denies all the allegations.
A Vote Leave spokesman said it had “twice been cleared on this matter by the Electoral Commission” adding: “As has been the case throughout, Vote Leave is obligated to review - to the extent it can after this long elapsed period since the referendum - all such allegations, and is doing so.
“We will as appropriate share any relevant findings with the Electoral Commission, again as we have always done.”
An Electoral Commission spokeswoman said: “The commission has a number of investigations open in relation to campaigners at the EU Referendum; it does not comment on live investigations.”