Labour veteran Alan Johnson hit out at Jeremy Corbyn and Momentum after the party's worst election performance since the 1930s.
Mr Johnson served in a number of Cabinet positions under Tony Blair's Labour government, including Home Secretary, and was also Shadow Chancellor when his party went into opposition in 2011.
Speaking on ITV news after a disastrous exit poll predicted a Boris Johnson landslide, and sat next to Momentum founder Jon Lansman, Mr Johnson laid the blame squarely at the feet of the left wing elements of the party.
He said: "I live in a working class community, and I have known Jon [Lansman] for many years now - he's been around from the Bennite days.
"And I'm afraid the working class have always been a big disappointment for Jon and his cult.
"Corbyn was a disaster on the doorstep. Everyone knew that he couldn't lead the working class out of paper bag."
Mr Lansman is a dedicated supporter of Jeremy Corbyn, sits on the party's powerful National Executive Committee, and runs campaigning group momentum.
Momentum has been instrumental in building support for Mr Corbyn within the Labour Party membership, which grew massively following reforms under Ed Miliband.
However, some say it has pushed the party further left and away from the centre ground that saw the party in power for 13 years.
Continuing his attack on Mr Lansman, Mr Johnson added: "Now Jon's developed this momentum group, this party-within-a-party.
"Aiming to keep the purity, the culture of betrayal goes on. You'll hear it now, more and more over the next few days as this little cult get their act together."
