Jeremy Corbyn has suggested a Labour Brexit deal could be preferable to remaining in the EU, putting himself on a collision course with activists and MPs pushing for the party to campaign for remain.

In an appearance on BBC One’s The Andrew Marr Show before a contentious debate on Brexit at the party’s conference in Brighton, Corbyn sought to play down Labour divisions after an aborted attempt to ditch Tom Watson’s job and the resignation of a key policy aide, Andrew Fisher.

When asked whether it was in Britain’s long-term interests to remain in the EU, the Labour leader said: “It depends on the agreement you have with the European Union outside.”

His suggestion that a Labour government could negotiate an exit deal that would be preferable to EU membership – and that he will reserve judgment until those negotiations are complete – will infuriate anti-Brexit activists.

He said: “We have consistently put forward what I believe to be a credible option, which is based on five pillars – the customs union, the trade relationship, protection of consumer and environmental rights, and of course the Good Friday agreement.”

If the EU27 agree to those demands, he said, “that would be a credible offer to put before the British people”.

More than 90 local constituency Labour parties (CLPs) have submitted motions on Brexit to the conference, most demanding their party support remain. These are due to be hammered out into a “composite” at a late-night meeting on Sunday.

But the national executive committee (NEC) is threatening to pre-empt those discussions by tabling its own policy statement – a draft version of which suggests deferring the decision on whether to support remain until a special conference to be held after a Labour government has negotiated a Brexit deal.

Corbyn made clear that was his position. “We would put both views and say look, this is the best deal we could get; this is the remain and hopefully reform option. These are the choices before you.”

He added: “The vast majority of Labour party supporters and members supported remain, but a significant minority voted the other way. The party, the people and the leader of this country should understand why people voted leave.”

Corbyn admitted he knew plans to ditch the role of deputy leader were under discussion, though insisted he was unaware that the “particular motion” would be launched on Friday night.

“I was not aware that the particular motion was going to be moved at that time but I knew they would be discussing options, so when I heard of this I then proposed a statement to the NEC which I put myself, which was that we should have a consultation about having two deputy leaders in the future, which would reflect gender and ethnic balance in our society.”

The attempt to abolish Watson’s post was launched by Jon Lansman, the founder of the pro-Corbyn campaign group Momentum, and supported by 16 other members of the party’s NEC.

Corbyn also confirmed that Fisher, his policy chief, was preparing to quit at the end of this year. Fisher sent a blistering memo, leaked to the Sunday Times, citing a “blizzard of lies and excuses” and apparently claimed that the highest ranks of the party were engaged in “class war”.

Corbyn said: “I’ve obviously seen the words that Andrew wrote, and I discussed them with him at some length, immediately.” He said Fisher would remain in post for the general election campaign. He added: “I think he said that because he was extremely distressed at that point about whatever was going on, discussions within the office, in that moment.”

Fisher was a central figure in compiling the 2017 general election manifesto. The Guardian understands he has recently been warning the shadow cabinet that Labour’s position of trying to appeal to both leave and remain is beginning to damage the party’s electoral standing.

“I’m taking the party into the general election to end austerity, to bring forward policies that bring about a better standard of living and better opportunities for people all across this country. I’m enjoying doing that,” Corbyn said – adding that “of course” he would serve a full term, if elected as prime minister.