JEREMY Corbyn has admitted to being “very nervous” after the Labour Party was the target of a "very serious cyber-attack".

The Labour leader made his comments after the party HQ said hackers had mounted a "sophisticated and large-scale cyber-attack" on Labour's digital platforms.

Some campaigning activities were temporarily slowed but the party’s systems were back up to speed by this morning.

A spokeswoman explained that the incident had been reported to the National Cyber Security Centre[NCSC] but the party made clear it was confident that no data breach had occurred.

The incident comes amid the continuing controversy over the UK Government’s decision not to publish a report by the Intelligence and Security Committee into alleged Russian interference into Britain’s democratic processes. The report is the result of an 18-month inquiry into illicit Russian activities in Britain.

Former Attorney General Dominic Grieve, who chairs the committee and has seen the report, has stressed its publication is essential ahead of the General Election because it contains information "germane" to voters.

But UK ministers have made clear that Whitehall’s “standard process” of checks, which takes a number of weeks, is being followed and that, because of General Election civil service purdah, the report cannot now be published until after polling day on December 12. It has been suggested the report was sent to Boris Johnson for his sign-off on October 17.

But the suspension of publication has led to some politicians to suspect the delay is happening because for political reasons; at the weekend it was claimed the report contained details about Russian donors to the Conservative Party.

Former US Secretary of State Hillary Clinton, whose presidential campaign against Donald Trump was supposedly hacked by the Russians, said it was “unfathomable” why the UK Government was not publishing the report before voters went to the polls.

She told the BBC: "I find it inexplicable your Government will not release a Government report about Russian influence; inexplicable and shameful. You're having an election.”

She added: "People deserve to know what is in that report. We had a somewhat similar problem in 2016."

A report into Russian interference in the US presidential election in 2016 found illegal interference from Moscow occurred in a "sweeping and systemic fashion", according to special counsel Robert Mueller.

On the campaign trail in Blackpool before heading to Scotland for a two-day visit, Mr Corbyn said: “We have a system in place in our office to protect us against these cyber-attacks but it was a very serious attack against us.

“So far as we're aware none of our information was downloaded and the attack was actually repulsed because we have an effective in-house developed system by people within our party.

"But if this is a sign of things to come in this election, I feel very nervous about it all because a cyber-attack against a political party in an election is suspicious, something one is very worried about.”

He pointed to the 2017 cyber-attack against the NHS, which was something that was “incredibly dangerous to the health records and the healthcare and treatment of potentially millions of people and so we do need far better defensive arrangements against cyber-attacks made against us”.

Mr Corbyn added: "As to who undertook the attack, we're looking into all that at the moment and we've obviously reported the attack to the National Cyber Security Centre and they will be investigating it as well."

A NCSC source suggested the cyber-attack on the Labour Party was low level and that there was no evidence of sponsored activity.

Labour sources confirmed it was a so-called distributed denial-of-service[DDoS] attack - one of the most common forms of attack - although they would not be drawn on who they thought might be responsible.

In a DDoS, hackers flood a target's online platforms with traffic from various sources, with the aim of slowing down access or causing websites to crash.

The last general election in 2017 was disrupted by the worldwide WannaCry attack, which hit hundreds of NHS trusts and GP practices, leading to thousands of appointments and operations being cancelled.

The NCSC subsequently attributed the attack to a shadowy North Korean crime organisation known as the Lazarus group.