David Cameron fired the starting gun today for a contest which could see Boris Johnson become Britain's next Prime Minister.
The former London mayor is expected to be the front runner to replace Mr Cameron as Conservative leader.
Mr Cameron announced his resignation in a speech in Downing Street.
Mr Johnson's decision in February to back the Leave campaign was a huge blow to the Prime Minister.
Mr Johnson's father Stanley said the referendum result meant his son was entitled to take part in a Tory leadership contest.