AP TELEVISION

FILE: London - 23 April 2008

++4:3++

1. Conservative candidate for Boris Johnson, then the Conservative candidate for Mayor of London, walking through market surrounded by media

2. Johnson walking onto stage and making speech

3. Various of people listening and Johnson making speech

POOL

FILE: London - 2 May 2008

++4:3++

4. Johnson and Ken Livingstone, the then-incumbent Mayor of London and Labour candidate, waiting for the results on stage

5. SOUNDBITE (English) Anthony Mayer, Greater London Returning Officer:

"I therefore officially declare Boris Johnson to be elected as the next mayor of London."

6. Wide of candidates on stage; supporters clapping and cheering

AP TELEVISION

London - 14 May 2016

7. Set up of Dr Tony Travers, political expert

8. SOUNDBITE (English) Dr Tony Travers, London School of Economics:

"Well there is no question that Boris Johnson is a high flying political figure. He has been mayor of London, he is now a member of parliament, he is a member of cabinet, and undoubtedly, he has as a longer term ambition a desire to get on presumably to be leader of his party, and therefore Prime Minister. Now, many people at the top of politics have that kind of ambition, few make it this obvious, or that obvious, others choose never to do it, but I think in his case he is an ambitious person who wants to get to the top."

UK POOL

FILE: York - 23 May 2016

9. Various of 'Vote Leave' campaign coach arriving, supporters cheering as Johnson, now Member of Parliament and leading "Brexit" campaigner, exits coach and delivers speech

AP TELEVISION

London - 14 May 2016

10. SOUNDBITE (English) Dr Tony Travers, London School of Economics:

"Well at the moment he is obviously the leading figure in the campaign to leave the EU, and I can't look into his mind and see what proportion of what motivated that is because he really wants to leave the EU and what proportion is motivated by a desire to move on within the Conservative Party towards being Prime Minister. But it would be naive not to assume that both objectives were present in what he is doing now, and he is be far the most charismatic and media literate of the pro-leave politicians - several others are pretty good at it, but he is particularly good at it - and he does have longer-term ambitions for sure. So the two things can never entirely be separated."

UK POOL

FILE: Bristol - 14 March 2016

11. Johnson talking to audience members and activists at "Vote Leave" event

AP TELEVISION - NO ACCESS UK (UK clients, please note this restriction)

FILE: London, UK - 1 August 2012

12. Johnson, dressed in suit and waving British flags, dangling from zip wire

AP TELEVISION

London - 14 May 2016

13. SOUNDBITE (English) Dr Tony Travers, London School of Economics:

"His detractors and critics often say he is not a serious person, that his approach to politics is humorous and freewheeling and not perhaps as thought through as other people; I'm not sure that's true. I think deep down he is a serious person, with serious objectives. Now the way it manifests itself doesn't look like many other politicians, but that's never been a barrier to getting to the top. You get to the top because - in this country anyway - because most of your colleagues in your party think you'll win them their seats in the next general election, and that will be the test that's applied to him as and when he goes forward to being potentially leader of his party."

POOL

FILE: London - 21 February 2016

14. SOUNDBITE (English) Boris Johnson, then-Mayor of London:

"I've decided after a huge amount of heartache because I did not want to do anything...the last thing I wanted was to go against (British Prime Minister) David Cameron or the government. But after a great deal of heartache, I don't think there is anything else I can do. I will be advocating 'Vote Leave' or whatever the team is called - I understand there are many of them - because I want a better deal for the people of this country."

POOL

FILE: London, UK - 22 February 2016

15. Johnson surrounded by reporters as he tries to cycle to City Hall

While still Mayor of London, UK legislator Boris Johnson declared his support for Britain's exit from the European Union and positioned himself in direct opposition to his Conservative Party leader and Prime Minister, David Cameron.

With the country's EU membership referendum taking place on Thursday, Johnson is set to find out whether his move, which many consider a play for the leadership, has worked.

The safe course for the ambitious former London mayor would have been to back Cameron, a long-time political ally, in his bid to keep Britain inside the 28-member bloc and let the prime minister sink or swim.

Instead, Johnson decided to become the most prominent figure in the "Vote Leave" campaign and use his considerable clout to try to pry Britain out of the EU - a result which would mostly likely also push Cameron out.

Many observers believe Cameron's days at 10 Downing Street would be numbered if his "remain" team lose the referendum vote.

Such a result would make Johnson a strong contender for the leadership role.

Long-time Johnson-watchers view his perch at the helm of the "leave" campaign through this Downing Street prism, said Tony Travers, a political scientist at the London School of Economics.

"Undoubtedly he has a longer-term ambition, a desire to be leader of his party and therefore prime minister," said Travers, who has tracked Johnson for years. "Now many people at the top of politics have that kind of ambition, (but) few make it that obvious."

Johnson denies he's eyeing the keys to 10 Downing Street, and has publicly said that Cameron should stay on even if Britain votes to leave the EU.

However, few take this position seriously - Johnson said in February it gave him "heartache" to break with Cameron over "Brexit," then jumped into the campaign with customary gusto.

The 52-year-old comes across as an unconventional politician despite having followed a classical political path, moving from elite colleges into journalism, on to Parliament, then City Hall, and finally back to Parliament and a minor Cabinet position.

"His detractors and critics often say he is not a serious person, that his approach to politics is humorous and freewheeling and perhaps not as thought through as other people," said Travers. "I'm not sure that's true. I think deep down he is a serious person, with serious objectives."

Johnson is not alone on the "leave" campaign stage.

UK Independence Party chief Nigel Farage has played a prominent role, despite recently coming under criticism for a provocative poster, and Justice Secretary Michael Gove has been a focal point as well.

They lack Johnson's flair for publicity, however.

Johnson has become the face of the "Brexit" campaign and, perhaps inevitably, the referendum campaign is seen by some as a Cameron versus Johnson race, with Downing Street as the prize.

Johnson's decision to break with Cameron over Brexit marks the first public split between the long-time friends and sometimes rivals.

They have known each since university days - the two were famously photographed in formal wear during their days as members of the exclusive Bullingdon Club at Oxford.

Throughout his career, Johnson has managed to surmount the sort of gaffes that have brought other politicians down.

Some believe this resilience would allow him to keep Downing Street in his long-term sights even if Britain votes to stick with Europe.

In his newspaper days, Johnson called Africans "piccaninnies" and referred to people from Papua New Guinea as cannibals.

As a Member of Parliament, he offended an entire British city when he complained that people from Liverpool were wallowing in "victim status" after a Liverpudlian was taken hostage and slain in Iraq.

He apologised - a lot - and seemed to be forgiven, but while he benefits from significant support from some quarters, there are others who would undoubtedly still wince at the prospect of Johnson reaching the top of the Westminster mountain.