The prime minister and Labour’s leader have marked the third anniversary of the Grenfell Tower fire with video messages as part of a virtual service.
Seventy-two people died as a small kitchen fire in the west London tower block turned into the most deadly domestic blaze since World War Two.
Boris Johnson said the country was working to ensure it never happened again.
Sir Keir Starmer pledged to do “everything” to make sure it did not.
The messages will be relayed to a virtual service later as the commemoration moves online due to the coronavirus. It will be hosted by the Bishop of Kensington.
In tribute to each person who died, bells of London churches will toll 72 times and green lights will glow from tower block windows.
Mr Johnson said: “We can all remember where we were three years ago today when we saw this tragedy unfolding on our screens and across the London skyline.”
He added: “As a nation, we are still dealing with the consequences of what happened and working to make sure it never happens again.
“While those affected by Grenfell are not able to gather in person, all of us in this country are with you in spirit.”
Labour has estimated 56,000 people were still living in homes wrapped in the same flammable cladding as Grenfell.
“In the midst of their suffering, the Grenfell community came together to campaign for justice, safe homes and change. Because no one should ever go through the loss and pain they experienced,” he said.
“But three years on and, unbelievably, tonight people will go to bed in unsafe homes.
“Three years on and there has been little justice or accountability. Three years on their campaign continues.
“I support Grenfell United. We can all learn from their strength and determination.”
The Fire Brigades Union (FBU) said high-rise residents faced a “postcode lottery” concerning how many firefighters would be sent to their building in the event of a blaze.
It said “many brigades would not be able to mobilise anywhere near the scale” that was needed to tackle the Grenfell Tower fire.
It added there was a large variation between the pre-determined attendance levels – the number of engines sent as standard to high-rise fires – for different brigades.
FBU general secretary, Matt Wrack, said there was “a good chance that the next Grenfell will be outside London, in an area where fewer resources are mobilised to a fire, and the loss of life could be worse still”.
Faith leaders will conduct sermons and reflections online throughout Sunday and from 22:30 BST, people in homes across the UK have been asked to shine a bright green light from their screens to show solidarity with the bereaved and survivors.
The public inquiry into the disaster was paused in March because of the pandemic and is due to restart on 6 July.