It is not every day you meet an interviewee that you have to greet with a bow. "When he walks into the room, you should refer to him as Your Majesty," advises David Dunkley, the King of Tonga's private secretary. "But don't worry – you don't have to do a full Polynesian bow down to the floor. His Majesty is not obsessed with formalities. He's very approachable."
There aren't many guides published on how to greet a Pacific island monarch, but an internet search the night before reveals that Tongans obey a strict code of ancient etiquette when addressing their royals including, I now know, making sure they never walk in front of them.
We are led up to the luxurious surroundings of a top-floor hotel suite in Knightsbridge, accompanied by advisers and a giant of a security guard who looks like he alone could give the entire Tongan rugby team a run for its money.
A few minutes later Siaosi Taufa'ahau Manumataongo Tuku'aho Tupou V, better known as King George Tupou V, sweeps into the room and warmly greets our respectful Western bows with smiles. Known for his love of bespoke couture he is dressed like the perfect country squire in a tailored double-breasted suit and a salmon pink shirt and sports an immaculate pencil moustache. His English accent, honed at Oxford and Sandhurst, is as spotless as his clothes.
"I try to come to Britain about once a year," the 61-year-old monarch explains, adding that this year's visit is a private trip to catch up with old chums from those carefree days when he was studying in the UK. "They are all scattered now in different areas and different walks of life, of course. But it's always good to see them."
King George, or "G5" as he is known to his friends, was first introduced to London as a wide-eyed teenager at the height of the Swinging 60s. But the Britain he knew was very much a world of Savile Row suits, officer training at Sandhurst and parties with friends who were also one day destined to become monarchs of far-flung lands.
"You have to understand of course that although we were teenagers growing up in London in the 1960s it was only really afterwards that we found out it was the place to be," he says. "People from America and Europe of our own age would come to London and marvel at something that we rather took for granted."
King George ascended Tonga's throne in 2006 following the death of his much loved father Taufa'ahau Tupou IV who, at 6ft 5in and 33 stone, was famously defined by the Guinness Book of Records as being the world's largest monarch. Taufa'ahau ruled the Pacific's last remaining monarchy with a mixture of paternalism and absolute control for more than four decades. His son was regarded in Tonga as something of a playboy – a rich kid, educated in boarding schools overseas who was detached from Tonga's largely impoverished and deeply Christian population.
Overseas he was renowned for eccentric hobbies (collecting toy soldiers, military uniforms and pith helmets) and behaviour. For official engagements, for instance, he preferred to be chauffeured in a pristinely upholstered London cab because, he once explained, it was "easier to get in and out of when you're wearing a sword".
Had he not been made Crown Prince, King George would have been happy to continue living his quiet but gilded life. But duty inevitably came calling. And life has been anything but quiet since taking Tonga's throne.
In November 2006, just a month after the death of King Taufa'ahau, Tonga's dusty capital Nuku'alofa erupted in pro-democracy riots which led to eight deaths and the destruction of half the city's business district. Throughout the latter stages of King Taufa'ahau's reign there had been growing calls to democratise Tonga's absolute monarchy and take power away from the country's deeply entrenched clan nobles who, alongside the royal family, still own the vast majority of Tonga's wealth. But any overt signs of democratic sentiment were generally tempered by the Tongan people's heartfelt respect for their king. It was one thing to want democracy, another thing entirely to hit the streets and demand it.
But with a new king on the throne – a person that the public had had little previous contact with – democracy activists were much more willing to take to the streets. The insecurity generated by the riots threw Tonga and its new monarch into the middle of a constitutional crisis.
The country could have lurched, like its Pacific neighbour Fiji, towards military dictatorship or an even greater entrenchment of the monarchy's absolute hold on power. Instead the king made it clear he was willing to relinquish his powers and turn Tonga into the world's next genuine democracy. He also agreed to sell off his substantial business interests, including Tonga's main power and communication companies. In the end King George's coronation ceremony was put off for two years to allow him to instead concentrate on finding a way of stewarding Tonga towards a democratic future. Barring any last minute quarrels with the nobles and their opponents in the pro-democracy movement, power will be handed to the Tongan people this November with the election of a new parliament and the replacement of an absolute monarchy with a constitutional one. This year, it seems, will be King George's last as the most powerful man in Tonga.
"I was educated in Europe and we were brought up on the principles of self-determination, self-expression and freedom of representation," he explains. "So it was something I always wanted to do. It's a question really of amending a 19th century constitution so you can retain the altruistic motivations of that era but express it in a 21st century idiom which has to be democracy."
Finding a solution that would keep everyone happy has been a particularly painstaking process. Take too much power away from Tonga's nobles and the king's reforms would have had little top-down support. But if the reforms didn't go far enough there was always the risk of further protests and riots.
A compromise has now been reached. Instead of having an upper house dominated by veto-happy nobles, nine seats in the new parliament will be reserved for clan leaders and 17 will be elected by the people.
"Once that is done," the king explains, "the parliament will elect a prime minister who I will appoint. He then gets to appoint a cabinet of 10 which means the government will always be in a minority as a hedge against not having an upper house."
For the Tongan people, the coming months will herald enormous change that will finally allow them to decide their own future. It will also, the king says, release a heavy weight from his own shoulders.
"My father was born and died in captivity," he explains. "I was also born in captivity. But these new democratic reforms will mean liberation for me as well."
Tonga: A Pacific relic
* Tonga is the Pacific's only remaining monarchy. The current dynasty – the Tu'i Kanokupolu – was founded by George Tupou I in 1875. Tonga remained free of colonial rule, becoming a British protectorate in 1900 but remaining independent. In 1970 it joined the Commonwealth.
* Throughout the 20th century, the country was dominated by two monarchs, Queen Salote Tupou III and her son Taufa'ahau Tupou IV, above, who each ruled for more than 40 years.
* Salote immediately won over the British press during the coronation of Queen Elizabeth II in 1953, because despite torrential rain she refused to have the roof of her carriage up.
* Taufa'ahau Tupou IV succeeded his mother in 1965.
* Since 1992 there have been increasing calls full democracy.
* Riots erupted in the Tongan capital in 2006 less than a month after Taufa'ahau's death. His son, George Tupou V, has since abandoned absolute powers and has set about making Tonga a democracy.