Labour was hit first, then came under a second digital bombardment, followed by a third attack on the website of the Conservative Party.
Two of Britain's main political parties were hit by cyberattacks on Tuesday that attempted to force them offline by overwhelming their systems just before ahead of a general election.
The "distributed denial of service" (DDoS) attacks came after Britain's security agencies warned that other countries, including Russia, may attempt to disrupt the Dec. 12 vote — a charge Moscow denies.
It also comes as Britain's government faces criticism over an unreleased parliamentary report on Russian interference in UK politics.
The Labour Party said it was subject to a cyberattack on its platforms but that the data breach attempt failed.
“We have experienced a sophisticated and large scale cyber attack on Labour digital platforms," a Labour Party spokesperson said in a statement to Euronews. "We took swift action and these attempts failed due to our robust security systems. The integrity of all our platforms was maintained and we are confident that no data breach occurred."
It said security procedures slowed down campaign activities but that they were restored. "We have reported the matter to the National Cyber Security Centre (NCSC)," the spokesperson said.
Just hours later, the party's website and other online services came under a second digital bombardment, followed by a third attack on the website of the governing Conservative Party.
"DDoS attacks are a common form of attack used by a very wide range of attackers. Mitigation techniques are available and worked in this case," a NCSC spokesman told Reuters.
Former US Secretary of State and 2016 presidential candidate Hillary Clinton weighed in on the report into alleged Russian interference, telling the BBC that it was "inexplicable and shameful" that it would not be published before the December 12 snap election.
"Every person who votes in this country deserves to see that report before your election happens," Clinton told the BBC.
The report was sent to Downing Street but needs further approval before it is released to the public, the government has said.
Dominic Grieve, the chair of Parliament's Intelligence and Security Committee, said in early November that the lack of response about a further delay was "unprecedented".