Official Brexit campaign Vote Leave should face criminal investigations over allegations it broke spending rules during the EU referendum, a former minister has said.

Labour's Ben Bradshaw said the public and Parliament would expect police and the National Crime Agency to become involved if the ultimate findings of an Electoral Commission (EC) investigation turn out to be as "serious" as those already leaked.

Bridget Phillipson, the Labour MP who is the spokeswoman for the Speaker's Committee on the Electoral Commission, told the Commons it was an "unusual step" for Vote Leave to comment on the elections watchdog's initial findings.

Matthew Elliott, the campaign group's former chief executive, said the EC had concluded that Vote Leave exceeded spending limits by making a donation to another Brexit-backing group.

The campaign, which was supported by senior Tories including Boris Johnson and Michael Gove, is expected to challenge the commission's findings when they are officially produced and has criticised the watchdog for its handling of the investigation.

Allegations against Vote Leave centre on a donation of almost £680,000 made by the campaign to a youth Brexit group called BeLeave.

It is alleged the money was used for the benefit of Vote Leave, to pay data firm Aggregate IQ for targeted messaging services.

If this cash was recorded as Vote Leave expenditure, it would take the campaign's spending over the £7 million limit, raising the prospect that electoral law had been breached - and could lead to a hefty fine.

Speaking in the Commons, pro-EU MP Mr Bradshaw said: "If the ultimate findings of the Electoral Commission investigation into law-breaking by the Leave campaign are as serious as the version that was leaked - disgracefully - by the Leave campaign itself, will she make absolutely clear to the Electoral Commission that this House and the public will expect full criminal investigations by the police and the National Crime Agency into this alleged wrongdoing, so the public can have confidence in the integrity of our referendum and electoral system?"

Ms Phillipson replied: "The commission has repeatedly called for an increase to the maximum penalty it can impose on political parties and other campaigners for a breach of the rules.

"In terms of the investigation that he refers to, it was an unusual step taken by the Leave organisation in sharing its views on the Electoral Commission's initial findings.

"The commission will give due consideration to any further representations made and will, at the earliest opportunity, publish a thorough and detailed closing report in order to provide a full and balanced account to both the public and to Parliament."