Why did Keir Starmer resign as Prime Minister?

It's become a familiar sight in British politics - the lectern outside 10 Downing Street, ready for another resignation speech.On Monday morning, Sir Keir Starmer became the sixth prime minister to stand down in almost a decade, despite on paper commanding a huge Labour majority.So, why was his departure inevitable? And what will be the Starmer legacy following his two years in office?Niall Paterson is joined by Sky's political correspondent Rob Powell.