Trafalgar Day 200 celebrations began with an early morning service conducted by the Navy chaplain on the deck of HMS Victory in Portsmouth.
Sailors stood in line during the ceremony on Lord Nelson's ship as a 60-strong Navy band performed.
After the ceremony, a wreath was laid to mark the spot where Nelson fell after being shot by a French sniper during the battle.
The finest crystal has been dusted down in preparation for the Queen's dinner in the Great Cabin on the Victory.
Sailors used flags to re-create Nelson's most famous address: "England expects that every man will do his duty."
A sombre ceremony at St Paul's Cathedral culminated in a wreath-laying ceremony at the foot of Nelson's tomb.
The mood was also sombre in Cadiz, southern Spain, where Defence Minister Jose Bono (R) inspected sailors and troops at a military parade.
Spanish soldiers sported the uniforms of their early 19th Century counterparts as a mark of respect during the parades.
Some of Nelson's descendants were in no mood for gloomy reflection - L/Cpl Brett Nelson (L), Cpl Arron Nelson (C) and Commando Craig Nelson (R) enjoyed the celebrations on board the Victory.
The celebrations moved into the evening as the Queen lit the first of a chain of beacons spread around the UK
A total of 1,000 beacons lit the night sky on Friday