The Prime Minister spoke on The Rest is Politics, a podcast that I listen to, saying that Russia interfered in the EU referendum on Brexit. Despite the outcry over this, he is right.
This does not invalidate the outcome. Russia has interfered in many elections, not just in the UK.
In 2017, The Times reported that Russian Twitter accounts promoted Brexit ahead of the referendum.
In 2018, the Guardian revealed that the Leave.EU campaign met Russian officials as many as eleven times. The US Senate also prepared a report detailing how Russia worked to promote Brexit.
In 2020, The Russia Report was published, which despite the allegations and evidence, deliberately did not look at Russian meddling in the Brexit vote.