Sir Keir Starmer has been dealt a major blow after the campaign group that helped spearhead his leadership bid started canvassing Labour members for his successor.

Labour Together, which was previously run by the Prime Minister’s chief of staff, Morgan McSweeney, started polling members on who would be best placed to replace Sir Keir as the party’s leader.

The survey, seen by The Times, asked who stands “the best chance of leading Labour to electoral victory at the next general election” in comparison to Sir Keir.

Members were also asked to rank who they would be likely to vote for in a leadership election out of a list of potential successors.

Health Secretary Wes Streeting, former Deputy Prime Minister Angela Rayner and Home Secretary Shabana Mahmood were among those named as possible candidates.

The remaining contenders included Education Secretary Bridget Phillipson, Energy Secretary Ed Miliband, the Prime Minister’s Chief Secretary Darren Jones, Greater Manchester Mayor Andy Burnham and Labour’s deputy leader Lucy Powell.

Labour Together, who offered respondents a £500 cash draw, also asked for potential candidates to be placed on a “left-right scale” of “very left wing” to “very right wing”.

The survey ended with a series of hypothetical head-to-head leadership choices.

However, internal polling about senior Labour figures is now unusual.

Labour Together is expected to convey the results of the survey to the party leadership and conduct further research on the views of the membership on a range of issues in the coming months.

There is no indication that Mr McSweeney or any potential candidates were aware of the survey, which remains open until December 15.

The comprehensive survey covers Labour’s handling of numerous policy areas likely to dominate any future leadership battle, including Gaza, housing, defence, climate change, education, the economy and immigration.

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Participants are also questioned about their motivations for joining Labour, their voting history in previous general and leadership elections, and their involvement in local campaigning activities.

Demographic information including education level and postcode is also collected.

Labour Together previously invested hundreds of thousands of pounds in internal polling under McSweeney’s leadership that proved instrumental in helping Sir Keir succeed Jeremy Corbyn in the 2020 leadership race.

During Mr Corbyn’s tenure as party leader, McSweeney utilised the organisation and its funding to conduct research that ultimately helped vanquish the left.

Josh Simons, who is now a Labour MP and Cabinet Office Minister, led the organisation until 2024.

However, Sir Keir’s premiership appears to be becoming more precarious by the day.

The Unite trade union is weighing whether to convene an emergency conference to decide on maintaining its affiliation with Labour.

Should the union sever ties, it would lose the ability to nominate candidates in leadership elections and its members would forfeit their voting rights alongside party members.

Unite was revealed this week to be Labour’s largest donor during the third quarter of this year, despite its antagonism towards Sir Keir.

Meanwhile, Ms Rayner is viewed as the “kingmaker” in any succession scenario, with Sir Keir attempting to woo her back into Cabinet.

However, Mr Steeting’s allies have also been looking to court Ms Rayner as part of a “joint ticket”.

The Health Secretary denied reports that he was plotting to replace Sir Keir last month.