Labour has launched a scathing attack on Jeremy Corbyn in a sign that Sir Keir Starmer is taking the threat posed by his former leader seriously. Mr Corbyn is set to become the leader of a group of six MPs in Parliament, giving him more numbers in the Commons than Reform or the Green Party, after independents elected on a platform of supporting Gaza said they were helping to build his new party.

Cabinet minister Peter Kyle, the Secretary of State for Science, Innovation and Technology, slammed Mr Corbyn as “not a serious politician”. He said: “The chaos and instability that he brought to our party I’m now viewing him wreak in his new party.” Mr Kyle added: “The thing that worries me the most about what he says is that he doesn’t want to spend money defending our country, that he is against the money that Labour is investing into the defence of our country. At the moment, these are the things that should fundamentally worry us about the words of Jeremy Corbyn.”

Mr Corbyn led Labour to defeat in the 2017 and 2019 general elections, although on both occasions the party received more votes than under Sir Keir’s leadership in 2024, when it won a landslide victory.

Speaking during a visit to a bin strike picket line in Birmingham, Mr Corbyn said 190,000 people had so far “signed up” for the party he launched this week with Coventry MP Zarah Sultana.

Polls have suggested it could immediately gain the support of 10% of voters and ex-Labour MP Ms Sultana said it should aim for “20 to 25 per cent and beyond”.

Independent MPs Ayoub Khan, Iqbal Mohamed, Adnan Hussain and Shockat Adam are also backing the new party, giving it six MPs once it is officially formed. A conference in the autumn is due to decide a name and constitution.

The six already work together as an “independent alliance” but are not recognised as a party within Parliament.

Some left-wing figures including journalist Owen Jones are calling for the new party to form an electoral pact with the Greens, which has the support of around 10% of voters according to recent polling.

But one Labour politician welcomed Mr Corbyn’s decision to launch his own party – saying it would encourage supporters of his style of politics to quit Labour.

Lord Glasman said: “For those of us in Labour who want the party to be a patriotic socialist party, it’s very good news because it removes a huge amount of static and noise, sort of student union politics, that sort of thing, and we can concentrate on being serious.

The national coordinator for the Revolutionary Communist Party announced she had signed up to join Mr Corbyn’s project. Fiona Lali told GB News: “Talking about an end to austerity, a free Palestine, genuine nationalisation – these are the things that people actually want.”