David Cameron caught singing a little tune to himself as he re-enters Number 10

David Cameron has been caught appearing to sing a little tune as he re-entered Number 10 after announcing Theresa May would be Prime Minister by Wednesday evening (Thursday NZ time).

After making the statement, Mr Cameron was picked up by an ITV microphone walking back into No 10 with his lapel microphone still on, singing to himself before saying "Right!"

Commentators on social media were quick to speculate that the tune sounded like the end of the theme from hit US TV drama The West Wing, others suggested it might be 'Bach's Air.'

Mr Cameron said he would tender his resignation to the Queen after he takes to the Despatch Box for a final appearance at Prime Minister's Questions.

He said Ms May will take the keys to No 10 by Wednesday evening (Thursday NZ time) and that he was "delighted" that the Home Secretary would succeed him in Downing Street.

Mr Cameron will chair his last Cabinet meeting tomorrow morning and appear in the Commons for the final time as premier when he goes head to head with Jeremy Corbyn at noon.

Before Ms May can become Prime Minister, Mr Cameron is required go to see the Queen to hand in his resignation and advise her to call for the person he thinks is best placed to command the confidence of the House of Commons.

Speaking outside Downing Street Mr Cameron said: "Tomorrow I will chair my last cabinet meeting. "On Wednesday I will attend the House of Commons for prime minister's questions.

"And then after that I expect to go to the Palace and offer my resignation, so we will have a new prime minister in that building behind me by Wednesday evening."