Sir Keir Starmer's leadership campaign has said it is "scurrilous" to suggest they breached data rules, after Labour reported allegations to the information commissioner.

Labour has handed accusations of the shadow Brexit secretary's team hacking into the party's membership database to the Information Commissioner's Office (ICO).

Sir Keir is seen as the frontrunner to succeed Jeremy Corbyn, but the allegation threatens to damage his prospects and drag the contest into bitter recriminations.

His campaign vice-chairman, Labour MP David Lammy, said on Monday there is "no substance at all" to the allegations.

"It didn't happen. There was no data-scraping. I can say categorically that this did not happen and it's denied fundamentally," he told BBC Radio 4's Today programme.

READ MORE: Keir Starmer's 'data scraping' allegations leaked to the press

"There was no attempt by the campaign to do this - it's scurrilous to suggest so and I'm quite sure that the information commissioner will find the allegations completely untrue."

The allegation came as Labour also investigated a complaint about rival candidate shadow business secretary Rebecca Long-Bailey's use of party data.

The National: Rebecca Long-Bailey

Lammy did not link the allegations, but described the report to the ICO, which was set up as an independent body to safeguard information rights, as "disappointing".

"I hope this isn't now a scramble to the bottom of the barrel because there's not been any scraping of data, it feels more about the barrel really," the Tottenham MP said.

Long-Bailey's camp called for the focus to get back onto policy and said the allegations against them arise from a "failure" to close an online system allowing access to Labour members' details at the end of the election.

"The investigation into Keir Starmer's campaign over an alleged data breach should not be allowed to distract from a moment of significant importance in determining the future direction of our party," a campaign spokesman said.

"As Rebecca's campaign has said previously, the accessibility of members' data stemmed from a failure to close Dialogue at the end of the general election campaign."

Labour general secretary Jennie Formby has written to all candidates following the reports about alleged misuse of membership data and party systems.

A Labour Party spokesman said: "The Labour Party takes its legal responsibilities for data protection, and the security and integrity of its data and systems, extremely seriously.

"We have written to all leadership candidates to remind them of their obligations under the law and to seek assurances that membership data will not be misused."

Corbyn's successor will be announced on April 4.