Thousands of people have come together to mark one week since the Westminster attack, in which four victims and the attacker died.
Police officers, doctors and hundreds of members of a Muslim youth association were among those walking across Westminster Bridge in memory.
Leeds, Leicester, Sheffield, Manchester and Birmingham also had events.
Earlier, inquests into the victims' deaths were opened and adjourned at Westminster Coroner's Court.
Khalid Masood killed three people when he drove his hire car into pedestrians on Westminster Bridge last Wednesday.
Aysha Frade, 44, who worked at a London sixth-form college; US tourist Kurt Cochran, 54, from Utah; and retired window cleaner Leslie Rhodes, 75, from south London died.
After crashing, Masood then fatally stabbed PC Keith Palmer outside Parliament, before being shot dead by police.
In a statement, Ms Frade's family said: "Our beloved Aysha; caring daughter, loving sister, amazing wife, irreplaceable aunt, thoughtful, supportive friend and the best and coolest of mummies.
"You were ripped away from our lives in the cruellest and most cowardly of ways. We now pray that you guide and protect not only us, but all of London, from further evil.
"You will always be remembered as our guardian angel who never shied away from facing up to bullies. There are no words to even begin to describe the crushing pain and eternal void left in our hearts."
In Westminster on Wednesday, acting commissioner of the Metropolitan Police Craig Mackey said: "This afternoon is about remembering the victims of last week's events.
"Our thoughts, our prayers, go out to everyone who was affected by the events last week."
Zafir Malik, an imam from the Ahmadiyya Muslim Youth Association, said his members were "here to show that we are united with our fellow countrymen and remembering those who have fallen, especially PC Keith Palmer".
As the vigil reached Parliament, dozens of people laid flowers on the side of the bridge, among them a man who was hurt in the attack.
At the scene
By Alex Therrien, BBC News
There was an atmosphere of solidarity as the silence was held on Westminster Bridge.
Just before the clock struck 14:40 BST, a group including police, children and faith leaders walked across the bridge, led by the banner "love for all, hatred for none".
When the silence finished, children and other members of the procession laid flowers near to where three pedestrians were killed by Masood.
Earlier, people held hands across the bridge in a symbol of unity.
Among those paying tribute was Danyal Ahmad, a trainee imam at the Baitul Futuh Mosque in south-west London.
The 21-year-old said his group, Ahmadiyya Muslim Youth Association, wanted to show that Islam was about "love, peace and compassion".
His brother, Zishan Ahmad, a 25-year-old imam, who also attended the memorial, added: "You can't divide London - we stand together.
"It doesn't matter if you are Muslim, Christian or Jew, or black, brown or any other race. London will never be divided."
Brendan O'Connor, from Holborn, central London, said the memorial service sent a message that those seeking to divide London are "not going to stop us".
The 59-year-old added: "There's love here. You can't kill love with hate. Love always conquers."
Speaking as the inquests into the deaths of the four victims opened earlier on Wednesday, senior coroner Dr Fiona Wilcox said it was a "tragic incident".
Senior investigating officer Det Supt John Crossley told the court Masood was armed with two knives and caused grave wounds when he attacked PC Palmer.
The father-of-two was wearing a stab vest, issued as routine to Metropolitan Police officers, but it was not enough to save him and he died at the scene.
Officers are examining a "large amount" of CCTV and footage taken by bystanders, which gives a "clear visual chronology" of how the 82-second incident unfolded.
He said: "Currently there are in excess of 1,500 potential witnesses, with accounts being taken from those who are deemed significant. This is currently in excess of 140."
The inquest heard details of how each of the victims had died.
Det Supt Crossley described how Masood, driving across Westminster Bridge, mounted the pavement twice in an apparently deliberate attempt to target pedestrians.
He crashed the car into the east perimeter railings of the Palace of Westminster, before going into the grounds to attack PC Palmer.
More than 35 people were injured in the attack. Twelve are still being treated in hospital, one of whom is in a coma.
The inquest into Masood's death will be opened and adjourned on Thursday.
In other developments:
- Commons Speaker John Bercow told MPs that two reviews of the incident will be held
- A preliminary report into how the perimeter of the parliamentary estate is secured and protected will be published by the end of April
- A review into the "lessons learned" from the response will report back by the end of June
- Earlier, acting Met Police commissioner Craig Mackey told London Assembly members last Wednesday was a "terrible" day but the capital's response had brought about "hope"
- He said the force had an "extraordinary" level of firearms capability and it was quickly made available after the attack
- The Met has announced that the funeral of PC Palmer will take place at Southwark Cathedral on 10 April
- He will receive a full police service funeral, which will be followed by a private cremation
Earlier, the family of a Romanian woman who fell into the Thames during the attack said they had been overwhelmed by "love, support and respect" for her.
Andreea Cristea, 29, was on holiday with her boyfriend Andrei Burnaz.
In a statement, the couple's families said Ms Cristea was still in a critical but stable condition in hospital. Mr Burnaz sustained a broken foot but has been discharged.
They added: "Our family is so grateful for the first responders, the medical personnel and the assistance of the UK government agencies."
The so-called Islamic State group has said it was behind Masood's attack, but police say they have so far found no evidence of an association with the group or al-Qaeda.
Two men were arrested in Birmingham under the Terrorism Act by police investigating the attack. One remains in custody after officers were granted warrants for further detention, while the other was released with no further action.