Anti-Brexit Labour activists and MPs are calling on Jeremy Corbyn to convene a special conference as soon as possible to set out the party’s plans for the next few critical weeks.

With Theresa May’s Brexit deal now due to come back to parliament for a vote in the week beginning 14 January, campaigners are keen to ensure Corbyn consults Labour members about the next steps.

Many would like him to shift immediately to a policy of supporting a second referendum.

Labour for a People’s Vote, the group that was instrumental in ensuring Brexit was discussed at Labour’s annual conference in September, is calling for a half-day recall for members to endorse a policy of backing a second referendum.

It has the support of Labour MPs including Alex Sobel, Paul Williams and Anna McMorrin.

Williams, the MP for Stockton South, said: “Time is running out … We need an emergency party conference to amend our policy to take account of the situation we find ourselves in, not the situation that we envisaged back in September.”

The carefully worded composite motion passed at Labour’s conference in Liverpool in September under the chairmanship of the shadow Brexit secretary, Keir Starmer, said the party should first vote against the prime minister’s deal, then push for a general election, and if that failed, consider a “public vote”.

Labour for a People’s Vote, which helped organise more than 100 local constituency Labour parties (CLPs) to submit motions to conference calling for a referendum, is now encouraging them to adopt a statement demanding a special conference.

“Whether or not a vote of no confidence is tabled and a general election called for, Labour needs to move quickly to clarify our position on a public vote,” the motion says.

“When the opportunity to lead presents itself, we believe the Labour party must be seen to take the initiative. Just as importantly, Labour members from across the party, including the vast majority of Momentum members, support a public vote.”

The statement has already been passed by five CLPs and is tabled for discussion in dozens more.

Policy motions outside the pre-conference season have no binding force, but the activists hope to send a symbolic message about what grassroots members want.

Labour’s national executive committee (NEC) has the power to convene a special conference to consider a specific issue. It last did so in March 2014, under Ed Miliband, to adopt new rules on selecting the party’s leader.

Anti-Brexit campaigners are concerned that Labour backed away from tabling a full-blown motion of no confidence in the government on Monday in part to avoid being trapped into supporting a referendum.

Instead, Corbyn tabled a vote of no confidence in the prime minister, which has no formal status under the Fixed-term Parliaments Act. That means the government is not obliged to set aside time to debate it, and even if it lost it would not bring down the government.

Corbyn’s spokesman has insisted the confidence motion does not imply automatic support for a referendum, even if a vote of no confidence is lost.

Other opposition parties, including the Liberal Democrats and Plaid Cymru, have tabled a full-blown no confidence motion, challenging Corbyn to add his signature – without which it will not be discussed until the new year.

A motion signed by the main opposition party leader must be granted time in parliament, and could trigger a general election.

The Lib Dem leader, Vince Cable, said: “The government has challenged the Labour party to table a real ‘no-confidence’ motion. We have now done that for them. Jeremy Corbyn need only add his name, and the debate and vote would happen before Christmas.”

The shadow housing minister, John Healey, said on Tuesday that Labour would table a full motion of confidence “when it is clear to the country the government has failed decisively”.