Reports by BBC says a minute’s silence will be held across the UK at midday to remember the 38 people – including 30 Britons – killed in the Tunisia beach attack a week ago.
Flags will be flown at half-mast over Whitehall and Buckingham Palace, while play at Wimbledon will be delayed.
The Queen and Prime Minister David Cameron will join the silence.
The first inquests into the deaths of the Britons will begin later, with the bodies of more of the dead expected to arrive back at RAF Brize Norton.
The foreign secretary has said all 30 British people killed have been identified. Philip Hammond said he was confident the figure was the final British death toll from the beach shootings in Sousse last Friday.
The Queen and Duke of Edinburgh will join staff in marking the silence at the University of Strathclyde during an official visit to open a new technology and innovation centre, while Mr Cameron will be in his Witney constituency in Oxfordshire.
A number of mosques are expected to participate in the silence, and many will also remember the victims during Friday prayers.
Police officers across the country will take part, the National Police Chiefs Council said.
And a special ceremony will also be held at the scene of the killings in Sousse, where dignitaries and tourists are expected to attend.
At Wimbledon, matches on the outdoor courts usually start at 11:30 BST but will begin at 12:15 to allow spectators and participants to take part in the silence.
Later, the first inquests will open at West London Coroner’s Court. Coroner Chinyere Inyama is expected to open and adjourn the hearings.
Further inquests are due to be opened at the court on Saturday and Sunday.
Post-mortem examinations will be carried out before the bodies are released to their families.
The bodies of 17 of the British victims have now been returned to the UK.
The repatriation of the dead is likely to take several days, with two further flights planned for Friday and Saturday.
The Foreign Office has now confirmed the deaths of Angie and Ray Fisher, aged 69 and 75 respectively, who were from Leicester and had been missing.
Thomson and First Choice has said all 30 British people killed were its customers.
“The whole company would like to extend our deepest sympathies to the family and friends of those involved in this tragic event,” it added.
“Our main focus now is to ensure the families of the deceased and our customers who have been injured receive all possible support at this incredibly difficult time.”
Other victims killed in the attack include three Irish citizens, two Germans, one Belgian, one Portuguese and one Russian national.
BBC correspondent Ben Brown, who is in Sousse, spoke to one Tunisian man who witnessed the attack and helped tourists to safety.
He said he feared for his life but when he realised the gunman was not interested in shooting Tunisians he linked arms with other local people to try to form a human barrier along the beach.
“You could only see one colour,” he said. “Everywhere was red.”
“I feel I could have done more. I tried my best… He is not Tunisian. We are not like that.”
He also pleaded with tourists not to abandon Tunisa. “Please keep coming. Don’t let him win,” he said.
