As Wes Streeting looks set to challenge Starmer as early as today, Angela Rayner could launch her own leadership bid after being cleared by HMRC over her tax affairs.
Allies of Health Secretary Streeting have told the BBC they expect him to formally launch his leadership challenge as early as today.
To be successful, he would need the backing of 81 Labour MPs to force a contest under the party rules.
Labour has been in turmoil since its catastrophic results in the English local elections and at Holyrood last week, leading to four ministers quitting and dozens more demanding Starmer resign.
Starmer has so far resisted calls to step down, but could be left with no choice should Streeting be successful.
It comes as former Deputy Prime Minister Angela Rayner this morning announced she has been cleared by HMRC over any wrongdoing regarding her tax affairs - potentially clearing the way for her to mount her own leadership challenge.
In a statement, she said HMRC has "cleared me of any wrongdoing," and that she has been exonerated "of the accusation that I deliberately sought to avoid tax".
She added: “When purchasing a home of my own with a mortgage, I did not own any other property and had no personal financial interest in the court-instructed trust set up to manage my son’s financial award. I was advised by experts that I should pay stamp duty at the standard rate.
“I set out to pay the correct amount of tax. I took reasonable care and acted in good faith, based on the expert advice I received, and HMRC has accepted this."
Rayner confirmed that she has now paid "every penny" that she owed.