"Welcome to our tax haven," a suited man wearing a bowler hat and proffering a wad of fake 100 pound bills said cheerily to a tourist in central London. "I'm not from here," the German woman responded with confusion. "I don't know anything about your tax haven."

The stunt the man was taking part in saw advocacy groups create a beach complete with palm trees and deck chairs in Trafalgar Square. It was just one of many demonstrations happening around UK Prime Minister David Cameron's international anti-corruption summit, taking place in nearby government offices at Lancaster House.

Oxfam, Action Aid, and Christian Aid set up a temporary "tax haven" in protest against the lack of transparency in Britain's offshore territories. (Photo by Sally Hayden/VICE News)

Attendees at the day-long event included US Secretary of State John Kerry, Nigerian President Muhammadu Buhari, Afghan President Ashraf Ghani, and Christine Lagarde, managing director of the International Monetary Fund.

Cameron has committed the UK to a public register of beneficial ownership, saying that secret offshore owners of British property will be made public. Five other countries announced today that they have also agreed to similar measures in their own territories: Afghanistan, Kenya, France, the Netherlands, and Nigeria.

The British prime minister also announced the creation of a global forum to step up international efforts to recover stolen assets being held overseas. The first meeting of the forum will be held in the US next year and will focus on returning assets to Nigeria, Ukraine, Sri Lanka, and Tunisia.

However, anti-corruption campaigners say this move doesn't go far enough, and that Cameron needs to make sure that British overseas territories themselves become more accountable by also agreeing to provide a public register.

In his opening remarks at Thursday's summit, Cameron said, "I believe that corruption is the cancer at the heart of so many problems we want to tackle in our world," something which costs countries around the world an estimated $1.26 trillion.

Speaking after him, Kerry said "corruption tears at the entire fabric of a society" and that poses as great a danger for a state as "extremists."

He noted that people around the world are angry because "the system is rigged," and said it was necessary to shut the doors to corruption and prove to people that they can trust in the system.

"We have to say no safe harbor anywhere. We have to get the global community to come together and say no impunity to corruption," Kerry said, while noting that when some countries tighten their laws others see that as an opportunity.

British Prime Minister David Cameron and Nigerian President Muhammadu Buhari at the opening of the anti-corruption summit in Lancaster House, London. (Photo by Facundo Arrizabalaga/EPA)

Meanwhile, Buhari said that "corruption is one of the greatest enemies of our time" because it "creates a system of patronage where the resources are shared out by a small elite while the majority are trapped in poverty."

"The global community must come up with mechanisms for stopping safe havens," the Nigerian president said, calling for a strategy to aid the monitoring and tracing of stolen assets or funds hidden in secret accounts abroad.

There was some commotion in the lead up to the summit after Cameron was overheard telling Queen Elizabeth on Tuesday: "Lots of leaders of some fantastically corrupt countries [are] coming to Britain." He continued: "Nigeria and Afghanistan, possibly the two most corrupt countries in the world."

In response Buhari — who has been publicly fighting corruption since he came to power last year — said: "I am not going to demand any apology from anybody. What I am demanding is the return of assets. What would I do with an apology? I need something tangible."

Nigeria ranks at 136 out of 167 in campaign group Transparency International's Corruption Perceptions Index while Afghanistan is at 166. Speaking on a later panel at the summit, Ghani called corruption an "enabler of political violence."

"We are asking you and all of Europe to go after drug money," he said. "We need very credible action because as long as the criminal economy persists, the networks, the actions we do [will not work]."

Alan Bell, the chief minister of the British Crown dependency the Isle of Man, also hit back at criticism, saying at the summit: "It is all very well to pick on small jurisdictions, unless the US joins this international agreement, unless the US does more and gives confidence to other jurisdictions... well, we need action not just fine words."

'I can imagine there are enormous pressures on the prime minister not to go the full way'

The long-awaited summit comes just over a month after the leak of the Panama Papers, which named Cameron's father as someone who had an offshore trust. Cameron himself later admitted to profiting from it.

In more bad timing for Cameron, on Thursday the UK's Electoral Commission also announced it would be taking his Conservative Party to court to force disclosure of documents about spending in the run-up to last year's British general election.

A total of 11 prime ministers and presidents attended the summit, and held a private breakfast before the sessions began.

Despite Cameron said on Tuesday that "because it's an anti-corruption summit everything has to be open... There are no closed-door sessions. It's all in front of the press." However, many accredited journalists weren't allowed into the event and instead had to watch the sessions on screens in a designated media area outside Lancaster House.

An anti-corruption demonstrator holds a wad of fake money in London's Trafalgar Square. (Photo by Sally Hayden/VICE News)

Speaking at Trafalgar Square's temporary beach as the summit continued, Barry Johnston, head of advocacy at Action Aid UK, told VICE News: "The fact that they're having a summit at all is a good thing. World leaders being forced to talk about [corruption] is a good thing."

However, he said the "elephant in the room" is "that we can't get the UK overseas tax havens to do the same... Why not now? What's stopping them?"

Another educational demonstration happening in London in the lead-up to the summit has been a set of "kleptocracy tours." Run twice a day by a group of anti-corruption activists including Roman Borisovich, from Ukraine, they've seen politicians and journalists taken on buses around houses run by foreign kleptocrats and questionable offshore companies, with guides who dub London "the money-laundering capital of the world."

On board Monday's morning tour, Luke Harding, a Guardian journalist who worked on the Panama Papers leak said: "In this great global scam the UK is the most complicit nation."

"The rich don't deal with tax anymore," he added. "It's for the suckers."

Meanwhile Russian anti-Putin activist Vladimir Ashkurov said that when he's reported cases of corruption by Russians in the UK "our words have been falling on deaf ears."

A man wearing a David Cameron mask from campaign group '38 Degrees' protests outside of Lancaster House in London. (Photo by Hannah McKay/EPA)

Alan Howarth, a Labour party politician, member of the UK's House of Lords and one of the passengers on the journey, told VICE News he thought there were problems getting representation from countries that do act as tax havens.

"What we actually need is less public grandstanding and more action, particularly with legislation," he said.

"I think it's a huge disappointment the British government has not made our overseas territories produce transparency and if that doesn't happen then we look hypocritical," William Wallace, a politician with the Liberal Democrats, said.

"There are hundreds of thousands of people in the UK who've got money in the Isle of Man or Bermuda or somewhere, and this is all very deeply embedded in our system. At least we need to control it and make it much more transparent."

Meanwhile, Labour's Jeff Rooker said: "I think David Cameron has done more than previous British prime ministers in opening up the corruption debate. Far more than Gordon Brown and Tony Blair." Yet he agreed that UK overseas territories "are using British law to cover up corrupt practices. All we're after is the same rules for British overseas territories for company ownership as we're going to have for company ownership in the UK. Who owns the companies? That's pretty important. And if you have transparency you're less likely to have corruption."

Rooker added: "I can imagine there are enormous pressures on the prime minister not to go the full way."