Tony Blair unleashed a tirade of criticism against Jeremy Corbyn’s leadership, saying he had turned Labour into a “glorified protest movement” and that the election rout had brought “shame” upon it.

The excoriating attack from the former Prime Minister, who from 1997 to 2005 won three consecutive General Elections, came as senior Labour figures began positioning themselves for the leadership contest with Emily Thornberry confirming her candidacy and Sir Keir Starmer, signalling he was preparing to stand.

After Labour’s worst election performance since 1935 Mr Blair did not mince his words in expressing his opinion of Mr Corbyn’s four-year leadership and his election strategy.

In a speech in central London, the former premier claimed Labour had adopted a "strategy for defeat".

He blamed Mr Corbyn’s "comic indecision" over Brexit and Labour's "wish-list" manifesto for turning the party he once led into an unelectable force.

"The result has brought shame on us,” declared Mr Blair. "We let our country down. To go into an election at any time with such a divergence between party and people is unacceptable.

"To do it at a time of national crisis, where a creditable Opposition is so essential for the national interest, is unforgivable."

Under Mr Corbyn, Labour had become a "glorified protest movement," claimed the 66-year-old ex-PM. He argued the party had been taken over by the "misguided ideology" of the radical Left, which had "never appealed to traditional Labour voters and never will".

Mr Blair continued: "Let us demolish the delusion that the manifesto was popular. The sentiment behind some of the policy reflected public anxieties, that's absolutely true, but in combination it was over 100 pages of wish-list.

"Any fool can promise everything for free. But the people weren't fooled. They know life isn't like that. And this loading-in of free broadband run by government at the last moment was the final confirmation of incredibility," he insisted.

The former party leader warned that his party would be "finished" if it did not transform itself into a "progressive modern coalition" with the ability to win and hold power again.

Later, Ms Thornberry, the Shadow Foreign Secretary, became the first senior party figure to declare her candidacy for the leadership.

The Remain-backing London MP was highly critical of Mr Corbyn for backing Boris Johnson's call for an election on Brexit, revealing she had written to him warning it would be an “act of catastrophic political folly”. She argued Labour, instead, should have insisted on a referendum on the Prime Minister’s proposed deal to “get the issue of Brexit out of the way before any General Election".

Her colleague, Sir Keir Starmer, the Shadow Brexit Secretary, confirmed he was "seriously considering" his own run as he warned Labour must not "oversteer" away from the left-wing politics of Mr Corbyn.

Rebecca Long-Bailey, the Shadow Business Secretary, is regarded as the favourite, having the support of senior Corbynite figures like John McDonnell, the Shadow Chancellor. The contest will be decided by the membership, which remains heavily pro-Corbyn.