Andy Burnham was officially installed as PM by the King today after Keir Starmer bowed out.The Labour leader was invited to form a Government at an audience in Buckingham Palace this afternoon. He will now head back to Downing Street, where crowds of aides and supporters have gathered to hear his first speech to the country.But the former Greater Manchester Mayor is already facing a crucial moment as he names his Cabinet this afternoon.The Labour Left is still clamouring for Ed Miliband to be made Chancellor, despite alarm from businesses and moderates. Markets have been calmer following speculation that Shabana Mahmood will get the role instead, but any surprises could prompt a panicky response.Meanwhile, the fates of big beasts such as Angela Rayner, Wes Streeting and Yvette Cooper are due to be decided.Resignations have begun, with prisons minister Lord Timpson announcing he is going alongside Sir Keir. Unusually, Mr Burnham was accompanied to meet the King by wife Marie-France van Heel. Buckingham Palace said in statement: 'His Majesty received in audience the Rt Hon Andrew Burnham MP and requested him to form a new Administration. 'The Rt Hon Andrew Burnham MP accepted The King's offer and kissed hands upon his appointment as Prime Minister and First Lord of the Treasury.'Ms Marie-France van Heel was also received by His Majesty.'The constitutional changeover came after Sir Keir used a farewell address outside No10 to insist he has not been a failure - despite only surviving two years following a huge election victory.Sir Keir said he was 'closing the book on my time', saying 'my work is done' and the country is 'stronger'. He insisted Mr Burnham - who orchestrated a coup to secure the leadership - would have his 'full support'.'I go with good grace, I go with a smile and I go proud of everything we have achieved,' he said, thanking wife Victoria and his family. Close Cabinet allies including David Lammy and Rachel Reeves had gathered with hundreds of aides in a sunny Downing Street to watch Sir Keir say goodbye. London Mayor Sadiq Khan was also present for the emotional moment. On another momentous day in UK politics:Mr Burnham has revealed his Alzheimer's-hit father does not know he is going to be PM, as he vows to overhaul social care;Eco-tycoon Dale Vince was spotted in Downing Street, amid confusion over whether the Government will allow more drilling in the North Sea; The new PM has hinted at an earlier end to the freeze on the basic rate tax threshold, without saying how it would be funded; Mr Burnham will become the first openly Catholic PM in around 500 years, with work-arounds put in place to protect the Church of England; Loudspeakers have been banned near Downing Street today after protesters blighted Sir Keir's speech announcing his resignation.Andy Burnham was officially installed as PM by the King today after Keir Starmer bowed out Unusually, Mr Burnham was accompanied to meet the King by wife Marie-France van Heel (pictured arriving at Buckingham Palace)Keir Starmer is giving a farewell address outside the famous black door of No10, just two years after winning an extraordinary election landslide