By Ian Dunt Follow @IanDunt
Remembrance events are taking place across London today as the country remembers the events of September 11th, 2001, when nearly 3,000 people were killed in a terrorist attack in New York.
Writing in the Sunday Mirror, US President Barack Obama said the US would "never forget" Britain's solidarity with his country in the aftermath of the attacks.
"We are touched that the UK will honour the victims again today – including by breaking with protocol and flying the union flag at half-mast at its embassy and consulates in the United States," he wrote.
The US president admitted that America's international relationships were damaged by the later military engagement in Iraq but celebrated the war in Afghanistan which followed shortly after the New York attacks.
"In the weeks after 9/11, we acted as an ¬international community. As part of a broad coalition, the US and the UK drove Al Qaeda from its training camps in Afghanistan, toppled the Taliban and gave the Afghan people a chance to live free from terror," he wrote.
"However, the years that followed were difficult and the spirit of global partnership frayed."
British foreign secretary William Hague said that, a decade on, Al-Qaida was a spent force, overtaken by the momentum and idealism of the Arab Spring.
"In the decade since the 2001 attacks on the United States, terrorists have succeeded only in the murder of innocents, often from among those they claim to represent," he said.
"Al Qaida is now weaker than at any time in the decade since 9/11 - and political progress through peaceful protest in the Middle East and North Africa has shown it to be increasingly irrelevant to the future."
He added: "The true expression of what people in the Muslim world aspire to was seen not at ground zero in 2001, but in squares and streets across the Middle East and North Africa this year."
Families of the 67 Britons who died gathered in central London for a service in Grosvenor Chapel this morning, close to the American embassy. Another ceremony was held nearby, at the September 11th Memorial gardens.
Another was organised at St Paul's Cathedral, where families of the victims will gather with fire, police and ambulance service representatives to celebrate the emergency service workers killed on that day in New York.
In the evening a service will take place in Westminster Abbey, brining the day's events to a close.
Outside the American embassy, tiny groups of extremist Muslims and far-right EDL marchers chanted slogans.
In Washington, there will be commemorations at the British embassy. In New York, the consol general will attend British Gardens in Hanover Square for a memorial council.
Major US cities are experiencing heightened security following warnings that terrorists could use the anniversary to launch another attack.
Metal barriers surround the area around lower Manhattan, where vehicles entering bridges and tunnels are being checked by police.
An official memorial featuring two reflecting pools each nearly an acre in size is being installed where the twin towers once stood.
The names of those who died in the attacks are inscribed on the sides of the pools.
Those names will also be read out in a service in New York.
There will be several pauses for silence - one for both moments that a place crashed into the Twin Towers, another for when a third plane hit the Pentagon and a fourth for when United 93 crash landed in a field.