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The government faced major political pressure over its planned cuts to winter fuel payments and welfare, including from the left of the Labour party - which were subsequently reversed and significantly watered-down.

On two separate occasions this week I have spoken privately to senior figures in both the Labour Party and the Conservative Party, who, unprompted, offered near identical reflections about how the next few years may pan out.

But all of those involved in the project believe there is a huge gap in the market to the left of Sir Keir Starmer's Labour Party, with millions of potential votes up for grabs.

And what would the arrival of a new socialist party mean for the Greens who have scooped up many left-wing voters in recent times - not to mention the Labour Party itself?

Corbyn's former shadow chancellor John McDonell said he was "dreadfully sorry to lose Zarah from the Labour Party" but is not expected to quit himself.