A sombre looking Prince Charles has laid a wreath for the Queen at the Cenotaph.
The Prince of Wales, who turns 73 today, led royals and politicians in laying wreaths of poppies at the war memorial.
Buckingham Palace earlier said the Queen would not be attending the service due to a sprained back.
Veterans have also gathered for the first time since 2019 after being told to stay away last year due to the pandemic.
Scroll down for the latest updates.
Members of the public gather to watch the Remembrance Service at the Guildhall Square in Portsmouth
12:53 , Sami Quadri
Thousands march in Manchester
12:50 , Sami Quadri
Crowds return as Manchester honours war dead in poignant Remembrance Sunday service https://t.co/uYqEtNp9o3
— Manchester News MEN (@MENnewsdesk) November 14, 2021
Nicola Sturgeon lays a wreath during the Remembrance Sunday service in Edinburgh
12:43 , Sami Quadri
Chief Executive of Fighting With Pride Craig Jones MBE poses with wreath
12:39 , Sami Quadri
Fighting with Pride are the first-ever LGBT+ group to march in the Remembrance Sunday parade at the Cenotaph.
The charity supports the mental health and wellbeing of LGBT+ veterans.
LGBT+ people were banned from serving in the armed forces until 2000.
It follows the Ministry of Defence's decision to return medals to veterans who had them stripped as a result of their sexual orientation or gender identity ahead of this Remembrance Sunday.
One of Britain’s last surviving D-Day veterans Harry Billinge says he will never forget fallen comrades
12:30 , Sami Quadri
— Dan Walker (@mrdanwalker) November 14, 2021
Young boy marches with veterans
12:22 , Sami Quadri
Boris Johnson pictured alongside Labour leader Keir Starmer and former Prime Ministers Tony Blair and Gordon Brown
12:20 , Sami Quadri
The Queen has missed Remembrance Sunday just six times in 69 years
12:16 , Sami Quadri
The Queen has missed Remembrance Sunday just six times in her 69 year reign (2 for pregnancy, 4 being abroad on Tour)
Full story on today’s announcement from Buckingham Palace of her “great regret” at having to pull out of today’s service at the Cenotaph.https://t.co/zqREvgOnm0
— Chris Ship (@chrisshipitv) November 14, 2021
Veterans begin marching
12:14 , Sami Quadri
Some 8,000 military veterans begin their march past the Cenotaph after the departure of the royal party. pic.twitter.com/J1cYzQnFZx
— Richard Palmer (@RoyalReporter) November 14, 2021
An emotional Duchess of Cornwall wipes a tear away
12:03 , Tammy Hughes
11:47 , Sami Quadri
The oldest and youngest people marching at the Remembrance Sunday parade at the Cenotaph have a gap of 90 years between them.
Veteran Roy Farmiloe, 98, is the oldest person at the parade while Evie Hebden was one of a number of eight-year-olds marching with the new youth column, christened Column Y.
Evie's father Royal Marine Ralph Hebden, 32, fell from a foggy cliff while going for a run near their home in Arbroath, Scotland in 2013.
The tragic accident occurred days before Evie's birth, The Liverpool Echo reported at the time.
Ralph was described at the inquest into his death as a "proud" marine who had served five tours of duty.
Prime Minister calls for us to “come together to remember those who sacrificed everything in service of our country".
11:28 , Sami Quadri
The Duke of Cambridge lays a wreath
11:18 , Sami Quadri
Prince Charles has laid a wreath for the Queen at the Cenotaph
11:15 , Sami Quadri
Queen will not be seen much in public as she enters new phase in her reign, says royal commentator
11:07 , Sami Quadri
Penny Junor has suggested Elizabeth II is entering a new phase of her reign in which she will not be seen as much in public.
Ms Junor said: "It's very sad for the Queen because this is the one event in the year that she really, really likes to be at.
"Remembering the war dead is a very, very important part for her annual calendar.
"The public will be very sad and anxious to hear of yet another setback but clearly she must follow the advice and get herself well."
She added: "It's not surprising because she is 95 years old.
"We're so used to seeing her out and about and looking years younger than she is that I think we've been lulled into thinking she can go on at this kind of pace forever.
"Clearly she can't. There comes a time in everybody's life when they have to admit that they are getting older and can't do the things that they perhaps want to do."
A member of the Household Cavalry appears to have fainted
11:03 , Tammy Hughes
D-Day veteran Joe Cattini, 98, pictured at the Horse Guards Parade
11:02 , Sami Quadri
Veterans from the Chelsea Pensioners
10:50 , Tammy Hughes
Queen will be disappointed to miss service
10:46 , Tammy Hughes
The Queen, who is head of the Armed Forces, lived through the Second World War as a teenager and attaches great importance to the poignant service and to commemorating the sacrifices made by fallen servicemen and women.
If she had attended today’s service it would have been her first in-person appearance since a reception for business leaders at Windsor Castle on October 19, after which she cancelled a trip to Northern Ireland on medical advice and spent a night in hospital.
Well-wishes for Queen
10:42 , Tammy Hughes
Service personnel attending the Remembrance Sunday ceremony at the Cenotaph wished the Queen well after learning that she was unable to attend.
Lance Corporal May Percival said: “My heart goes out to her and her family. I wish her well and the best.”
RAF Nurse Officer Stephen Andor said: “I wish her well. The Queen has very strong links to the military. She is the head of the armed forces.
“I think that every single member of the military wishes her well.”
Boris Johnson leaves Downing Street
10:39 , Tammy Hughes
Military veterans line up ahead of the march past for the Remembrance Sunday service
10:36 , Tammy Hughes
Concerns that car journey would make sprain worse
10:34 , Tammy Hughes
It is understood the sprain is recent and there were concerns over the impact of a car journey and a period of standing on her recovery.
The Queen is said to be deeply disappointed over her absence and she will remain at Windsor Castle.
Buckingham Palace statement in full
10:31 , Tammy Hughes
“The Queen, having sprained her back, has decided this morning with great regret that she will not be able to attend today’s Remembrance Sunday service at the Cenotaph. Her Majesty is disappointed that she will miss the service.
“As in previous years, a wreath will be laid on Her Majesty’s behalf by The Prince of Wales.
“His Royal Highness, along with the Duchess of Cornwall, the Duke and Duchess of Cambridge, the Earl and Countess of Wessex, the Princess Royal and Vice Admiral Sir Tim Laurence, the Duke and Duchess of Gloucester, the Duke of Kent and Princess Alexandra will be present at the Cenotaph today as planned.”
Queen has not received hospital treatment for her back
10:27 , Tammy Hughes
It is understood the Queen has not received hospital treatment for her back and the injury is unrelated to recent medical advice for her to rest.
The Queen is said to regard the Remembrance Service at the Cenotaph as one of the most significant engagements of the year.
It is also understood she plans to continue with her schedule of light duties over the coming week.