Tony Booth, the actor best known for his role in Till Death Us Do Part also accused Mr Blair of going into Kosovo with his "hands tied, blindfolded and telling your opponents your plans".

It is the first time the new head of Equity, the actors' union, has spoken out since his son-in-law came to power at the 1997 general election.

Tony Blair married Cherie Booth in 1980

Mr Booth, the father of the prime minister's wife Cherie Booth QC, revealed he sat in the Commons gallery during the debates on disability bill, which led to Labour's largest backbench rebellion.

"I sit in the gallery and after 15 minutes I'm in a total rage," he told The Guardian.

"I always want to shout, 'How dare you say that? What the hell's going on?'

"They sit there and say it's easy to live off 60 of 70 quid a week. Well, I know how hard it is because I've done it."

Attempts to cut benefits and force people to take low-paying jobs ran contrary to the actor's understanding of the Labour movement.

"Look, I joined the Labour Party because it was dedicated to helping the weak, the old, the poor and justice.

"To pick on the disabled and single mothers is not in my opinion what we're about. They're the ones who need our help."

Attacks from all generations

Tony Booth: A long-standing critic of political leaders

Mr Booth's two other main complaints were the abolition of the option of trial by jury in so-called "either way" cases and the handling of the Kosovo air strikes.

"The trial by jury thing really had me jumping up and down. It's our right. It's the right we fought for 800 years," he said.

On Kosovo, he agreed Nato had needed to act, but insisted the allies bungled the attack strategically.

"You don't go into a conflict with your hands tied, blindfolded and telling your opponents your plans do you?

"You don't say, 'We are not going to use ground forces, so don't worry'."

'Vision and decency'

Tony Booth describes his daughter, Cherie, as "shy"

Mr Booth further disclosed the prime minister is not only under fire from the older generation of his in-laws.

"Everyone has an opinion in our family. Even our grandchildren. You should hear what they say to Tony and Cherie. I just think, go for it, kids."

He went on to urge members of the public to harangue the prime minister if they meet him during a public visit.

"They shouldn't say, 'How are you, it's a nice day', they should say, 'What about disability, what about asylum'."

But the prime minister's father-in-law finally had a few good words, if not for his son-in-laws actions then at least for his intention.