Services will be held in London and Glasgow, as well as on mainland Europe at cemeteries and memorials marking the outbreak of the “war to end all wars”.
A special wreath was flown yesterday from Montrose Air Station Heritage Centre – the first UK military airbase – to northern France and war memorial in Amiens.
On 3 August, 1914, pilots of Royal Flying Corps’ II (AC) Squadron flew from Montrose Air Station in their biplanes for the final time.
The wreath was taken in a replica SE5, similar to those flown by the squadron, to RAF Leuchars from which it was then taken to Devon by of II (AC) Squadron’s Tornados. The last leg of the wreath’s journey to Amiens will be in a replica BE2.
Scotland lost an estimated 100,000 men during the war out of the British total of 745,000 of “the Lost Generation”.
At 10am, a national service of commemoration will be held at Glasgow Cathedral, attended by the Prince of Wales, David Cameron and other dignitaries before a procession to the cenotaph in George Square for a wreath-laying service. There will then be a march-past.
A service in Cointe, Liege, Belgium, will be attended by international leaders and the Duke and Duchess of Cambridge this morning, while the Queen will be at a service at Crathie Kirk near Balmoral and Prince Philip at Sandringham, Norfolk.
Amongst other services will be a service near Mons, Belgium, attended by members of the Royal Family, Mr Cameron and others before a national “lights out” between 10pm and 11pm with just a single light or candle to mark the start of the war.
A solemn commemoration at Westminster Abbey will end in the extinguishing of candles one by one except for the single burning oil lamp on the tomb of the Unknown Warrior.
The great-niece of a First World War soldier will join dignitaries including the Duke and Duchess of Cambridge at ceremony near Mons. Helen Jones will be the first member of her family to visit the grave of her great-uncle Private George Bellamy as she attends a special evening ceremony at St Symphorien military cemetery.
The 57-year-old plans to lay some flowers on the grave of Pte Bellamy, of 2nd Battalion the Royal Irish Regiment, in a “thank you” for the sacrifice made by him, and millions of other soldiers.
Mrs Jones said the first thing she knew about her great-uncle was when her brother Paul, who had started carrying out his own research into Pte Bellamy, contacted her while she was on holiday in Thailand to say he had been invited to the ceremony but could not go, and said she should go.
The NHS administrator, from Westwoodside, north Lincolnshire, said: “My dad never spoke about this, it just was never discussed at all so I had no idea.George was 23 I think when he went to war, but he must have been a professional soldier because he went out with the British Expeditionary Force.”
He died on August 26 1914 –just days into the Battle of Mons – she said.
“I really want to lay some flowers on George’s grave,” she said. “They just gave everything. A whole generation almost of young men just disappeared, we just can’t credit it.”
Yesterday, French president Francois Hollande commemorated the 100th anniversary of World War I and paid homage to those who lost their lives after Germany declared war on France on 3 August 1914. But he recalled that former enemies France and Germany put aside their differences to pave the way for peace – and that others do the same.
German president Joachim Gauck joined the French leader for the ceremony – the first time Germany’s head of state has attended.
Mr Hollande also put in place a foundation stone for a museum at Hartmannswillerkop that will open in 2017.