Sir Keir Starmer developed a "10-year plan" for power that was then brushed to one side when he entered No10, a former adviser has told GB News.
Peter Hyman, who served as a senior aide to Sir Keir for two years ahead of the 2024 general election, said this was "a mistake".
He was speaking after Sir Tony, whom Mr Hyman also advised during his Downing Street days, criticised Sir Keir's team for having "no properly thought-through analysis of how the world was changing and what was meant for policy" in a 6,000-word essay.
Labour came into power with five missions to rebuild Britain, including kickstarting economic growth, making Britain a clean energy superpower, taking back our streets, breaking down barriers to opportunity and building an NHS fit for the future.
Mr Hyman told Chopper's Political Podcast: "We worked – a number of us with Keir – on what we called missions for Government.
"And they were 10-year plans, and they were about doing some of what Tony was saying, which is bashing down the bureaucracy of Government and getting things done.
"And that's what the missions were about.
"Now, what I regret is, and what I think the Government hasn't done sufficiently, is carried on 'mission Government' in Government.
Sir Keir Starmer outside No10 after winning the 2024 General Election
|GETTY
"So it's lost that mission. We spent two years trying to get that architecture of a reformed government, and then it was a brush to one side. That was a mistake."
Sir Keir, along with his potential leadership challengers, ex-Health Secretary Wes Streeting and Greater Manchester Mayor Andy Burnham, largely dismissed Sir Tony's criticism this week.
However, Mr Hyman said: "We need to listen to him because he's won three elections.
"Tony Blair was the most successful Labour leader. So everything and anything or everything he's got to say is worth having a look at."
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Peter Hyman discussed Labour's plan for power with GB News
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He added: "This is a well-argued essay. He talks about the challenges of the future.
"He is the best. When I was working for him, he was the best leader I've come across who could look to the future, spot the trends, and get ahead of the game."
Mr Hyman said Sir Tony was right to say that the UK needs to embrace artificial intelligence and "be about aspiration and opportunity".
He added: "And that's always been a thread of his. And I share that view.
Sir Keir Starmer celebrating victory after the 2024 General Election | PA"So a lot of it is about how you have a politics of greater clarity. You make big arguments, you try and win them.
"Most of all, he's saying the rise of populism is down to governments not getting things done.
"And so he wants governments to think more clearly about reinventing the state and cutting through the bureaucracy."
Mr Hyman, who went into teaching after working in No10, published a report today which laid bare the crisis affecting 16-24 year olds who are not in employment, education or training.
Peter Hyman sat down with Christopher Hope
|GB NEWS
Titled "Inside the Mind of a Young Neet", it attacks a system which presents young people "with too many snakes and not enough ladders".
Mr Hyman told GB News: "We've got to change the curriculum in schools.
"The Government's been too timid on that curriculum and assessment.
"There's got to be better pathways, they've got to be signposted, and they've got to have status.
"So a young person doesn't think, If I'm not going to university, I don't know what I'm doing,' or 'I'm a loser.'"