Former SDP Gang of Four on Jeremy Corbyn's Labour
The three surviving members of the SDP Gang of Four say Jeremy Corbyn should step down as leader before the general election in 2020.
Baroness Shirley Williams said she believed Mr Corbyn did not want to be prime minister - while Lord Owen predicted he would quit in autumn 2019.
Lord Rodgers said he thought Mr Corbyn was "a very dangerous man".
Mr Corbyn has repeatedly insisted he will not step down and has been elected leader twice.
Earlier this week he said that was sure Labour could win a general election.
Many in the Labour Party blame the Gang of Four's defection and the establishment of the SDP for Labour's defeats at the 1983 and 1987 elections.
The three veteran politicians gave their predictions in a rare joint interview, with BBC 5 Live's Emma Barnett.
The trio split from the Labour Party in 1981 when - together with Roy Jenkins, who died in 2003 - they broke away to form the SDP.
What was the Social Democratic Party?
The party formed by the Gang of Four joined forces with the Liberal Party to create the Liberal-SDP Alliance in autumn 1981.
It turned the 1983 election into a three party contest, getting 25.4% of the vote - although only getting 23 MPs because of the first-past-the-post system. It won 22.6% of votes in 1987 and got 22 MPs.
After the election, Liberal Party leader David Steel proposed an official merger with the SDP and while most of the SDP's membership voted in favour of the merger, its leader David Owen remained adamantly opposed to it.
The merged party lives on as the Liberal Democrats.
The events that led up to their decision to quit Labour have been dramatised in a new play - Limehouse - which had its press preview on Wednesday evening, attended by all three.
Reunited for the first time in several years, the group talked about the origins of the SDP and the echoes of that decision in today's Labour Party.
Asked if Labour MPs should break away to form a new party, Lady Williams said: "I think there'll be a battle. I think a really major battle in the Labour Party is inescapable."
She added that she believed Mr Corbyn does not actually want to become prime minister.
"He is a decent man... but I don't think he actually wants the responsibility at all."
Lord Rodgers gave a different take on the Labour leader. "I don't share the view about Corbyn," he said. "I came across him many years ago and he was, I thought, a very dangerous man on the far left."
Asked if he would advise Labour MPs to break away, Lord Owen said: "No, I wouldn't. I think they are very strong in the parliamentary party and they should stick together in the parliamentary party."
But he predicted the party would ditch Mr Corbyn. "Jeremy Corbyn is a decent person and I think he will stand down before the next election - and I think Labour will choose somebody who is more acceptable to the electorate."