The Labour Party has been hit by a second cyber attack in the space of 24 hours.
Hackers attempted to force the party's web services offline at around 1.20pm today, a source told Reuters.
It happened just hours after Labour revealed a first attack had happened yesterday afternoon.
The source said both attacks were "very unsophisticated" distributed denial-of-service (DDoS) attacks which try to take down target websites by flooding them with malicious traffic.
Party sources have confirmed the latest incident, but provided no further information.
Describing yesterday's incident Jeremy 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 speaking in Blackpool the Labour leader expressed concern about possible future attacks.
He said: "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."
In May 2017 the WannaCry malware attack clobbered hospitals, businesses and banks, leading to 7,000 NHS appointments being cancelled.
Mr Corbyn said: "A cyber attack, as happened in 2017 against our NHS, is something that is 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."
He 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."
Experts warned that the incident should set alarm bells ringing ahead of December 12’s poll.
Professor Anthony Glees, director of Buckingham University’s Centre for Security and Intelligence Studies, told the Mirror: “You have to ask yourself who benefits?“This could have been some teenagers in a basement, but we really can’t rule out a political motive.
“In the US election cyber attacks were used very successfully by third parties to undermine the process.
“Dirty tricks can win or lose elections and as we move into a cyber age it is something we need to be more aware of.”
Cranfield University’s Dr Duncan Hodges said the attacks were “co-ordinated and large scale” if not complex.
He added: “We shouldn’t be confident that this is over, we have seen this type of attack used as cover for further activities.
“With the delicate political environment, it doesn’t take much to create disruption.
“We have increasingly seen attacks on our democracies and our election apparatus, in France before the election sustained attacks were successfully defended, and we have seen cyber-attack situations in the US around elections too.
“Small attacks, equivalent to physically knocking over a political party’s sign, are one thing, but larger co-ordinated attacks could have more detrimental consequences.”
It comes as Tories face increasing pressure to release a report examining Russian influence in British politics.
Although there has been no indication of the precise contents of the report, it will assess the threat posed by Moscow to Britain's democratic processes following an 18-month inquiry into illicit Russian activities in Britain.
Moscow has repeatedly denied Western allegations of election interference and a person with knowledge of the matter said an initial investigation had found nothing to link the Labour Party attack to a foreign state.
In the build up to the general election on December 12, parties will be reliant on digital methods of reaching voters on an unprecedented scale.
Last month the National Cyber Security Centre revealed that more than 650 attacks had been made against the UK in a year.
These included exposing a campaign by the GRU, the Russian military intelligence service, of “indiscriminate and reckless cyber attacks targeting political institutions, businesses, media and sport”.
