Labour has suffered a second cyber attack on its digital platforms within the space of 24 hours, the party said.
A party spokesperson said the latest distributed denial-of-service (DDoS) incident was being dealt with "quickly and efficiently".
Earlier, leader Jeremy Corbyn expressed concern after the party experienced what it described as a "sophisticated and large scale" DDoS attack on Monday.
However, it is understood that the attacks were relatively "low level".
The National Cyber Security Centre confirmed it would not be investigating the matter further, while a source said there was no evidence of "state-sponsored activity".
DDoS attacks - where hackers flood a target's online platforms with traffic from various sources, causing them to slow or crash - are considered relatively common.
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Following the latest incident, a Labour spokesperson said: "We have ongoing security processes in place to protect our platforms, so users may be experiencing some differences.
"We are dealing with this quickly and efficiently."
Speaking at a campaign event in Blackpool following the first incident, Mr Corbyn said he was "nervous" about what it could mean for the rest of the General Election campaign.
"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," he said.
"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."
Labour said the initial attack had failed due to the "robust security systems" which it had put in place and that it was confident there had not been any data breach.
They said: "Our systems have been slow the whole time so I didn't notice anything particularly new. Not entirely sure what we were meant to have experienced.”
Paul Brand has also obtained a copy of the email sent to Labour staff this morning.
The NCSC said the party had informed it of the attack and had taken the "necessary steps" to deal with it.
"The attack was not successful and the incident is now closed," a spokesman said.
While DDoS attacks are among the most common form of cyber attacks, experts said they could vary enormously in the level of sophistication.
Dr Duncan Hodges, senior lecturer in cyber operations at Cranfield University, said it was possible to "hire" the capability to mount such attacks for as little as 100 dollars, but that did not mean they were insignificant.
"I wouldn't call this attack sophisticated, but it is certainly co-ordinated and large scale in that it involved multiple attacks," he said following the first incident.
"We shouldn't be confident that this is over, we have seen this type of attack used as cover for further activities.
"Any attack on our democratic process or that affects the ability to conduct a fair election, and hence respect the outcome of that democratic process, we should take very seriously."
Edward Apeh, principal academic in computing at Bournemouth University, said identifying the perpetrators may not be easy.
"Attribution for this problem here right now will be very hard, except if a group comes out and says they are responsible - it's going to be very hard to attribute the attack to any particular person," he said.