Former Downing Street grandee Baroness Camilla Cavendish says the Prime Minister has 'made a terrible mistake' and 'should reinstate' sacked Olly Robbins to the Foreign Office.

In damning comments today on Sir Keir Starmer's premiership, Baroness Cavendish, who was head of former Prime Minister David Cameron's Policy Unit at Number 10, said the PM was in 'a lot of trouble' and would 'find it hard to come back from his error'.

She also warned the Mandelson affair, which saw Foreign Office Head Robbins sacked over alleged vetting failures, 'had brought out Starmer's deep character flaws and lack of judgment' and slammed him for 'totally failing to deliver the manifesto the country had elected him on'.

The crossbench peer also sounded a note of serious concern about the UK's relationship with the US and said they 'no longer saw us as a serious player'.

Speaking to the BBC today following her comments in today's Financial Times where she said the 'power is draining away from Sir Keir Starmer's Downing Street', the baroness, who is still involved in government as a non-executive director at the Department of Health and Social Care, said: 'Some people think this is a media storm but it actually isn't because in sacking Olly Robbins, and I do feel very strongly that he should be reinstated.

'I think what the country saw on Tuesday was the top official and the best of the civil service refusing to throw anyone else under the bus.

'He was asked "will you name the people in the private office?" and he said "I'm not going to scapegoat anyone else".

'I think that was the moment when the country thought that actually the Prime Minister has a serial record of blaming other people and scapegoating other people and in sacking Robbins, the Prime Minister jumped very quickly to a conclusion with the full information.

'That was a terrible mistake to be quite honest and he's going to find it hard to come back from.'

Speaking to Radio 4's Today programme, she also compared Starmer to Boris Johnson and said there was a 'vacuum at the centre' of both men while denying suggestions the country was simply 'ungovernable' and it was not Starmer's fault.

She said: 'I don't think Britain is ungovernable at all. The peculiarity of our constitution is that the system looks upwards to the Prime Minister so it does depend enormously on the quality of the Prime Minister – with Boris Johnson there was a vacuum at centre and bizarrely there is with Keir Starmer.'

Warning there was a problem when 'the guy at the top doesn't make decisions', she said: 'With the North Sea, he is letting his Energy Secretary fight it out with the Treasury and on Housing he has got planning reforms through but he is not making all the other important changes that need to be made in the construction industry.

'Every single time on welfare reforms Downing Street's job is to get difficult things through Parliament and to make a case for them but he didn't do that. He is not fulfilling the job.

'The peculiar thing to me is that this is a man who drove through really important changes in the Labour Party before he came to power and crushed the Corbyn left - and he did a really good job of that - and so I think a lot of his colleagues are just completely stymied by the fact that he is quite disdainful of politics and he doesn't really want to get involved.'

Asked about the King's visit to America and the issues Donald Trump says he is looking forward to discussing with him, she said: 'Donald Trump ought to be discussing those with the British Prime Minister.

'I was in America a week ago and they are not interested in Britain any more. We are not seen as a serious player.

'Our chancellor was on her way to the IMF meeting in Washington when she decided to bash Donald Trump. These things are totally unserious.

'Keir Starmer wanted to be seen as a serious Prime Minister. He has got a lot of kudos over standing up to Trump over Iran not letting them use bases and then letting them use bases. 

'I think we should all be asking ourselves what is actually in the national interest.'