Former Tory MP Andrew Bridgen announced he is formally suing Matt Hancock for libel on Wednesday in a row over a vaccines tweet.
The North West Leicestershire MP also confirmed he had joined actor Laurence Fox's Reclaim party after being kicked out of the Conservatives for expressing controversial views on Covid jabs.
Mr Hancock, who was suspended from the Tories for appearing on I'm a Celebrity... Get Me Out of Here, condemned the comments as "antisemitic".
At an event on Wednesday morning, Mr Bridgen said he had submitted a defamation claim to the High Court, saying the former health secretary's comments were an attempt to "shut down valid concerns expressed by me".
He later took a seat on the opposition benches for Prime Minister’s Questions in the House of Commons.
Earlier this year, Mr Bridgen tweeted: “We know the ‘vaccines’ are causing serious harms and now it’s becoming increasingly clear how they are doing it. No wonder so many people are ill since vaccination.
“As one consultant cardiologist said to me this is the biggest crime against humanity since the Holocaust."
Sharing a news article about the rise in excess deaths Britain is seeing as the NHS battles staffing shortages and strikes, he wrote: "Is the failure of the NHS also responsible for the current excess deaths in all other countries that administered the gene therapy mRNA ‘vaccines’?"
More than 650,000 deaths were registered in the UK last year- 9 per cent more than 2019.
NHS delays, flu cases and the aftermaths of the pandemic have been blamed for the rise.
Mr Bridgen was also suspended from the House of Commons earlier this year over his “careless and cavalier attitude” to lobbying rules and suggesting the woman investigating him could be bribed with a peerage.
Responding to the news that Mr Bridgen has joined the Reclaim Party, Liberal Democrat Deputy Leader Daisy Cooper MP said: “Andrew Bridgen and his misinformation have absolutely no place in the House of Commons and now his defection to a failed fringe political party cements it.
"If Bridgen wants to sit as an MP for this party he should do the right thing - resign and call a by-election."
