The King has urged Britons to remember the “extraordinary courage and compassion” amid the horrors of the July 7 London bombings, while British PM Keir Starmer said the country will unite to remember the lives lost.

In a message to mark the 20th anniversary of the attacks, the King said on Monday (Australian time) comfort could be taken from the “spirit of unity” in London and the country more broadly, which had allowed the nation to heal.

Meanwhile, Starmer said “those who tried to divide us failed” adding “we stood together then, and we stand together now”.

On July 7, 2005, four suicide bombers struck London’s transport network, killing 52 people and injuring more than 770 on three Tube trains and a bus.

The King asked for the country to reaffirm its commitment to building a society of all faiths and backgrounds, standing against those who seek to divide us.

“Today, as we mark 20 years since the tragic events of 7th July 2005, my heartfelt thoughts and special prayers remain with all those whose lives were forever changed on that terrible summer’s day,” he said.

“We remember with profound sadness the 52 innocent people who were killed in senseless acts of evil – and the enduring grief of their loved ones.

“We recall, too, the hundreds more who carry physical and psychological scars, and pray that their suffering may ease as the years pass.”

The King said countless stories of extraordinary courage and compassion that emerged from the darkness of that day should also be remembered.

“The selfless bravery of our emergency services, transport workers, and fellow citizens who rushed towards danger to help strangers reminds us of the very best of humanity in the face of the very worst.”

Other members of the royal family are to join services and memorials to mark the anniversary.

-AAP