The Express understands Wes Streeting privately informed Sir Keir Starmer he is building a case to succeed him as Prime Minister - as the embattled leader confronts what could be the decisive 24 hours of his premiership.
Streeting has reportedly signalled to Downing Street that he will not move against Sir Keir directly, but is assembling what allies call a leadership "case" to deploy the moment a contest is triggered - and stands ready to launch a full campaign should the Prime Minister be removed.
The internal turmoil threatens to drown out Starmer's Monday address, in which he will pledge to deepen ties with the EU and acknowledge that "incremental change won't cut it."
Catherine West, a backbench former minister, is understood to be preparing to mount a formal challenge on Monday. She is backed by a growing bloc - 42 MPs at the last count, including figures who were previously considered loyalists — who have demanded Sir Keir's resignation or a departure timetable.
Rayner chose Sunday to make her move, calling publicly for Burnham to be given a path back to the Commons. The former deputy leader — making her first public statement since Thursday's rout - said it was time to "bring our best players into Parliament", reports the Telegraph.
She also criticised the "toxic culture of cronyism" in No 10 and warned it might be Labour's "last chance" to reverse its fortunes. However, she stopped short of joining the more than 40 MPs who have publicly demanded Sir Keir's resignation.
Rayner is thought to be planning to run if a contest takes place but is not expected to challenge Sir Keir imminently.
Meanwhile, Burnham's allies are attempting to delay any contest until he has returned to Parliament, warning MPs they risk handing Downing Street to Labour's Right if they move too quickly.
Electability against Farage will be the backbone of any Streeting pitch - with his team pointing to Labour's hold on Redbridge, covering his east London patch, as proof he can fend off Reform from both directions.
By contrast, Streeting's allies argue Rayner's Reform-busting credentials are undermined by the collapse of Labour's vote in Tameside — a council overlapping her own Greater Manchester seat.
One Streeting ally told The Telegraph: "Wes has made it clear to No 10 that he won't challenge Keir, but he is preparing a case if it all falls apart. Like most of the party, he thinks Keir is owed the chance to set out how he's going to turn things around this week. He's not plotting."
The ally added: "This week has shown he can win. The results in Redbridge show that Wes can beat challengers on both the Left and Right. If there's a contest, the next leader of the Labour Party has to be someone who can keep Farage out of No 10."
If Streeting does launch a full campaign, it is expected to be built around five "pillars" including specific policy proposals. Thursday's publication of NHS waiting time figures is expected to bolster his case further, with data anticipated to show the health service at or near the 65 per cent target for non-urgent treatment within 18 weeks.
Express understands Streeting's most recent conversation with Sir Keir about the leadership took place before the scale of Thursday's losses became clear.
