Britons up and down the country will take part in a one minute's silence today to remember the 38 people who were killed in the attack on a beach in Tunisia last week.
The Queen will lead the silence, which will take place at midday, with the Duke of Edinburgh at the University of Strathclyde David Cameron will also take part from his constituency in Witney.
Flags at both Buckingham Palace and Whitehall will be flown at half-mast.
Play at Wimbledon, which usually begins at 11:30am, will be delayed for the commemoration.
Police officers across the country will take part, the National Police Chiefs Council said.
A special ceremony will also be held at the scene of the killings in Sousse. Londoners are also being invited to pay tribute to the victims in a book of condolence, which is being made available at South Council's Tooley Street base.
A number of mosques are expected to participate in the silence, and many will also remember the victims, 30 of whom were British, during Friday prayers.
More bodies are expected to be flown back to RAF Brize Norton today and the first inquests are expected to begin today at West London Coroner's Court. So far 17 bodies have been repatriated.
Coroner Chinyere Inyama is expected to open and adjourn the hearings, with further inquests due to start on Saturday and Sunday.
Thomson and First Choice, which are owned by Tui Travel, have 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," the group 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."