Speculation of his leadership ambitions surfaced last year when – having backed Ed Miliband for leader and served on his front bench – he was talked of as a possible successor.

He did not stand then but has declined to rule out running for the top job since, saying in January it would be an “incredible honour” to leader the party.

Born in Morecambe, Lancashire, Mr Smith is the son of a Welsh historian, Prof Dai Smith, and was educated at Barry boys’ comprehensive school in south Wales.

He studied History and French at University of Sussex before working for the BBC as a producer on Radio Four’s Today programme and the Welsh political show Dragons Eye.

Then came a well-paid job as a lobbyist for the pharmaceuticals company Pfizer – which produces, among other drugs, Viagra – and a role advising Paul Murphy, the former Northern Ireland secretary.

While Mr Smith insists he would have voted against the Iraq War today, the man he was spinning for backed the invasion, which could be tricky to argue away during the leadership race.

He first tried to enter Parliament in 2006, contesting the seat of Blaenau Gwent in south Wales, before becoming MP for Pontypridd in 2010.

Within months he was on the frontbench, first as shadow Welsh minster and then as shadow secretary on the same brief as he rapidly rose through Mr Miliband’s senior team.

After last year’s leadership race – he backed Andy Burnham, not Mr Corbyn – he was made shadow work and pensions secretary and has impressed colleagues with assured media performances and loyalty to Mr Corbyn.

Seen as being on the soft-Left politically, Mr Smith was not one of the first resignations after the EU referendum but decided to go after a tense meeting with the leadership.

Critics see him as a political chameleon and Westminster insider who put his ego before party interests in launching a leadership bid while many others from the 2010 intake held back.

Supporters insist he is an assured and principle leader in waiting who can command more support across the party than his moderate rival Angela Eagle.

By the autumn, we should know which camp Labour members put him in.