A service will take place at St Paul’s Cathedral later to mark the 10th anniversary of the terrorist attacks that killed 52 people in London.
The families of those who died in the bombings of three Tube trains and a bus will attend, along with some of those injured on 7 July 2005.
A minute’s silence will be held during the service and on London’s transport network at 11:30 BST.
Prince William will also attend a service at Hyde Park’s 7 July Memorial.
The attack by four suicide bombers linked to al-Qaeda and carrying rucksacks of explosives was the worst single terrorist atrocity on British soil.
Just after 08:50 on 7 July 2005 three explosions took place on the Underground – 26 died in a bombing at Russell Square on the Piccadilly line; while on the Circle Line six died in an explosion at Edgware Road, and seven lost their lives at Aldgate.
Almost an hour later a fourth device was set off on a number 30 double-decker bus in Tavistock Square, killing 13 people.
The names of the 52 victims will be read out at the national service of commemoration at St Paul’s Cathedral, which begins at 11:00 BST.
More than 700 people were also injured in the attacks.
Prime Minister David Cameron said: “Ten years on from the 7/7 London attacks, the threat from terrorism continues to be as real as it is deadly – the murder of 30 innocent Britons whilst holidaying in Tunisia is a brutal reminder of that fact. But we will never be cowed by terrorism.”
The Duke Of York and London mayor Boris Johnson will be among those at St Paul’s, where prayers will be led by priests who helped minister people in the aftermath of the attacks.
The minute’s silence will be preceded by announcements on London’s transport network. Tube trains and buses are expected to be halted, if they can do so safely, while the occasion is observed.
At St Paul’s, the silence will end with petals being released from the dome, and four candles will be lit – one for each of the four blast sites.
The silence will also be observed at Wimbledon, where play will begin at 11:45 BST instead of 11:00.
Meanwhile, commuters are being urged to “walk together” by finishing their morning bus or Underground commute one stop early and travelling the last few minutes by foot.
The initiative aims to encourage them to remember the victims of 7 July 2005 and show unity.
It recalls the hours after the attacks when thousands of people had to return home by foot because public transport had been shut down.
Ten years on from the bombings, the anniversary events will begin at 08:50 BST with the laying of wreaths by figures including representatives from the police and emergency services at the memorial in Hyde Park.
The monument comprising 52 stainless steel pillars, each representing a victim, was unveiled in 2009.
At Tavistock Square, where 110 people were also injured, there will be a short service of remembrance.
The mayor of Camden, local MP Sir Keir Starmer, and Dr Peter Holden and Keith Ward from the British Medical Association – whose staff rushed out of their nearby headquarters to attend to the injured in 2005 – will be in attendance, along with Philip Nelson and the Reverend Anne Stevens from the 7/7 Memorial Trust.
In the afternoon, the Duke of Cambridge will join victims’ families, survivors, and ambulance and fire brigade employees who were working 10 years ago, for a service at the Hyde Park memorial, where there will be songs, recitals and a reading.
By Peter Hunt, BBC correspondent
This anniversary, like all the anniversaries, is set to be a painful day for the bereaved.
One mother, whose son was killed, has spoken of how, initially, she felt that the colour had gone out of the world and life was “awfully long and awfully grey”.
Those who have lost relatives and those who were injured have been invited to the service at St Paul’s Cathedral and to the more informal memorial event in Hyde Park this afternoon.
In the park, at the end, they will lay yellow gerberas – the flower is said to symbolise innocence and purity.
The bombings were carried out by Mohammad Sidique Khan, 30, Shehzad Tanweer, 22, Hasib Hussain, 18, and Germaine Lindsay, 19. The group had links to al-Qaeda in Pakistan and Afghanistan.
Speaking ahead of the anniversary, the country’s most senior counter-terrorism officer, Metropolitan Police Assistant Commissioner Mark Rowley, said the rise of Islamic State militants meant the UK was now facing a “very different” threat.
“We’ve seen another step change in terrorism in the way it works and connects across the world in the last couple of years,” he said.
The UK’s terror threat level was raised from “substantial” to “severe” in August 2014 in response to conflicts in Iraq and Syria.
Meanwhile, the head of MI5, Andrew Parker, described the “disgusting” events of 7 July 2005 as an “enduring reminder” of what his organisation “is striving every day to prevent”.
“In the preceding months, there had been a degree of scepticism about the terrorism threat in the media: surely it couldn’t happen here?” he said.
“The fact of 7/7 ended those arguments and led to a step change in the nation’s counter-terrorism defences.”
A total of 52 people lost their lives when four suicide bombers attacked central London 10 years ago. Here are their stories.