Angela Rayner is poised to run for deputy Labour leader and support her friend Rebecca Long-Bailey to succeed Jeremy Corbyn.

In one of the most significant developments in the race to replace Corbyn, the education secretary opted not to stand for the top job herself.

Instead she has decided to throw her weight behind shadow business secretary Long-Bailey, her flatmate and fellow Greater Manchester MP.

The post of deputy leader was vacated by Tom Watson before the election and a packed field of contenders could include Richard Burgon, Ian Lavery and Dawn Butler.

HuffPost UK has learned that Rayner is exploring a deputy leadership bid but there won’t be any formal announcement until later this week.

Rayner was seen as one of the few successes of the Labour campaign and was praised for her performance in final TV debates.

But she and Long-Bailey entered parliament together in 2015 and colleagues have said they would never stand against each other.

Long-Bailey- who has yet to publicly declare – is almost certain to become the only ’Corbyn candidat in the leadership race, with the backing of leftwingers most loyal to the current leader.

Under party rules, contenders need nominations from 10% of MPs in order to stand.

With a rump of just 203 MPs remaining after its rout in the general election, no more than 35 of them are see as on the pro-Corbyn ‘Campaign’ group wing of the party.

Both Long-Bailey and Rayner could become front-runners as they will hope to swing both trade unions and the grassroots members group Momentum behind them.

When asked by HuffPost UK recently if she and Long-Bailey would have a ‘Granita Pact’, named after the Islington restaurant where Gordon Brown agreed to step aside for Tony Blair, Rayner replied that the issue had not come up.

“We don’t even talk about it. We are just too knackered doing our day job that we genuinely don’t. We talk about stuff like what we are getting for tea. Becky tries to make me eat more veg. She literally does. I call her Mum,” she said.

Corbyn is set to step down some time in mid-March after a leadership and deputy leadership contest run in parallel from January 7.

Long-Bailey’s main challenge for the leader post may come from Lisa Nandy, if she can pick up unions and Momentum members.

Other contenders expected to enter the leadership race are Keir Starmer, Jess Phillips and possibly David Lammy. Barry Gardiner is said to be scoping out at shot at the top job too.