Jeremy Corbyn has blocked an attempt to deselect a heavily pregnant Labour MP, his office has revealed.

The Labour leader stepped in after a local activist called for Ellie Reeves to be ousted from her Lewisham West constituency this week.

The party member suggested Reeves should face a ‘trigger’ ballot as a punishment for criticising a decision to allow controversial fellow MP Chris Williamson back into the party.

But Corbyn’s office has now written to the Parliamentary Labour Party (PLP) to clarify that any pregnant MP would be exempt from re-selection processes used to confirm candidates for the next general election.

In a separate move, the activist critical of Reeves has decided to withdraw a plan to table a motion of no confidence in her.

Reeves was one of 120 MPs and peers who signed a letter from deputy leader Tom Watson last week, calling for Williamson’s immediate suspension from the parliamentary party.

She and others had expressed their concern that anti-semitism claims against him had not been properly investigated.

The move to deselect Reeves was swiftly condemned, with shadow health secretary Jon Ashworth saying the “ludicrous” no confidence motion should be “binned”.

On Wednesday morning, Watson tweeted that it was an attempt by activists to “bully another pregnant MP out of the party”, a reference to Luciana Berger’s departure earlier this year.

Reeves is 22 weeks pregnant but is not yet on maternity leave, meaning that she was in theory subject to trigger ballots like other sitting MPs. 

But Corbyn’s spokesman said that guidelines on reselection would be clarified to make clear that MPs like Reeves would be exempt.

“We are now starting the process of trigger ballots and reselections and that process will go on as quickly as possible. But in the case of pregnant women that would not take place,” he said. ““It’s not about lifting the process of accountability. It’s about taking account of the pregnancy.”

A spokeswoman added: “The leader’s office has written to the PLP to make clear that if any pregnant women who have not yet gone on maternity leave would like to discuss timescales on the reselection process to contact their regional director or the general secretary. 

“No pregnant woman who does not want to go through the reselection process while they are pregnant will have to do so.”

Reeves told PoliticsHome: “I was really pleased to receive a message from LOTO [the Leader of the Opposition’s office] this morning saying the leader has stated he does not support the no confidence vote. This was the support I was hoping for when I contacted them about it on Monday.”

A Labour source said: “It would be wrong to bring a motion of no confidence against a pregnant MP who will soon be on maternity leave. No motion has been formally moved or tabled. And in any case, motions of no confidence have no formal standing and do not result in trigger ballots.”

Fellow backbencher Stella Creasy, who is also pregnant, has clashed with leftwingers in her local party but the new rules suggest she would survive any attempt to remove her.

Cobyn’s spokesman stressed that in the event of a snap election, the normal process of trigger ballots – which allow local members to pick another candidate – would not apply. 

All MPs, including pregnant and suspended MPs, would have their fate determined by the ruling National Executive Committee (NEC) if their candidacy had not been sorted out before a snap election.

“The NEC would have to take the decision about what to do with those cases, it’s not just about pregnant women it would be about people who hadn’t been at that point through the trigger ballot reselection process,” the spokesman said.