How did Gary Lineker and the BBC’s impartiality crisis unfold?

Gary Lineker will return to present Match of the Day after he was taken off air amid an impartiality row following his criticism of the government's new asylum policy. 
BBC director general Tim Davie said an independent review of BBC social media guidelines would be carried out - and denied the BBC had backed down.  The BBC’s analysis editor Ros Atkins examines what the BBC has called ‘grey areas’ in its impartiality guidance after the corporation struck a deal with Lineker over his controversial tweets.