Johnson, who was born in New York, said the 67 Britons who died in the attacks are "a symbol of the eternal friendship between the UK and the US
British Prime Minister Boris Johnson said Friday the perpetrators of the September 11, 2001 attacks failed to destroy Western values, in a video message for the 20th anniversary of 9/11.
"We can now say with the perspective of 20 years that they (the jihadists) failed to shake our belief in freedom and democracy," he said in the message delivered ahead of the anniversary on Saturday.
"They failed to drive our nations apart, or cause us to abandon our values, or to live in permanent fear."
Johnson, who was born in New York, said the 67 Britons who died in the attacks are "a symbol of the eternal friendship between the UK and the US".
He insisted that Britain's resolve to uphold the values of freedom and democracy was not shaken by last month's withdrawal of Nato forces from Afghanistan, which saw the Taliban regain power.
The previous Taliban regime sheltered Osama bin Laden and his Al-Qaeda movement, which carried out the 9/11 attacks.
"Recent events in Afghanistan only strengthen our determination to remember those who were taken from us," Johnson said.
The fact that Britons and Americans were coming together to mourn the dead in 2001 "demonstrates the failure of terrorism and the strength of the bonds between us".
The US presented the UK with a sculpture made of twisted metal debris from the remains of the World Trade Center in New York.
As London mayor, Johnson unveiled the sculpture in the city in 2011, but it was later removed and is now on display at the Queen Elizabeth Olympic Park in east London.