Servicemen and women who died during the Afghanistan campaign and veterans who fought in the conflict will be remembered at a service of commemoration today.

At St Paul's Cathedral, the Queen, joined by Prime Minister David Cameron, senior members of the Royal Family and veterans, will lead the nation in honouring all those who fought to free Afghanistan from the Taliban.

The Duke of Edinburgh, the Prince of Wales, the Duchess of Cornwall, the Duke of Cambridge, his heavily-pregnant wife Kate, and Prince Harry - who served two tours during the conflict - will also attend the ceremony, held to mark the end of combat operations in the country.

The families of some of those killed will take part in the commemorations, and veterans of the 13-year campaign will march past the cathedral in a parade after the service.

Deputy Prime Minister Nick Clegg and Defence Secretary Michael Fallon will attend with the Earl and Countess of Wessex and the Duke of Gloucester.

Afghan President Ashraf Ghani told the BBC the 453 UK troops had "paid the ultimate sacrifice to enable us to live in freedom, in hope for peace, prosperity and dignity".

Today's commemoration comes after Tony Blair admitted that he had not foreseen just how long the struggle in Afghanistan would last when he first deployed troops in the wake of the 9/11 attacks.

In an interview with Forces TV, the former prime minister said that even now it was not properly understood just how much more there was to be done.

"I think we have not yet understood the depth of this problem, the scale of it, and the need for a comprehensive strategy to deal with it," he said.

"It is not just Islamic State in Iraq and Syria ... It is happening day in and day out - there are thousands of people losing their lives every few weeks."

He said he believed his decision to deploy British troops in Afghanistan had been justified, although he acknowledged that families who had lost loved ones may feel differently.

"I always felt that it was right and justified that we were there in Afghanistan, that we were fighting both to remove the Taliban and then to try and stabilise the country. But there is nothing that's really possible to say that could provide true consolation for family of someone who has lost their life," he said.

David Murray, chief executive of armed forces charity SSAFA, said the nature of the issues that those who served in the conflict are dealing with will take time to deal with.

He said: "Experience tells us that the full impact of Afghanistan is yet to be seen. The very nature of the issues those who served in Afghanistan are dealing with will take some time to unravel.

"SSAFA is already supporting many of those who fought in Afghanistan and their families. The charity is guiding bereaved families through the grieving process, aiding those whose worlds have been turned upside down by life-altering injuries and reaching out to those suffering with the mental effects of war."

He added: "As Afghanistan makes the transfer from the front pages to the history books, let us not forget that our forces have been doing their duty on our behalf, to keep us safe. They have had our backs, now is the time for us to have theirs.''

Almost 150,000 UK personnel served in the Afghanistan conflict, and 453 British men and women died in the fight against the Taliban insurgency.

Their sacrifice will be honoured during the service, which will feature an address by the Archbishop of Canterbury, the Most Reverend Justin Welby.

The Archbishop will bless a cross made of shell casings which adorned a memorial wall in the main allied base in Afghanistan, Camp Bastion, before it is later moved to the Royal British Legion's National Memorial Arboretum.

Representatives of other nations which took part in the Nato-led International Security Assistance Force will also attend. After the service there will be a parade through the City of London to the Guildhall.

Five detachments will be made up of serving personnel from the Army, RAF, Royal Navy and the Royal Marines, with a sixth of up to 400 veterans from the conflict, brought together by the Royal British Legion (RBL).

They will march past St Paul's accompanied by military bands and pipes and drums, with Charles taking the royal salute.

Aircraft from the campaign, including Chinook, Apache and Sea King helicopters, as well as Hercules transport planes and Tornado attack jets, will roar over the parade in their own salute.

Members of the Royal Family will later meet those who took part in the commemorations or served in Afghanistan during a series of receptions.

Similar services will also be held at military bases, cathedrals and churches across the country, as well as in Germany for personnel serving there.

A spokesman for the RBL said: "The end of combat operations in Afghanistan provides us the opportunity to reflect on the 453 service personnel who lost their lives in that conflict and the many thousands more who served their country under trying conditions.

"The Legion salutes them and stands ready to preserve their memory and their welfare.''

Following the announcement of the service last month, Mr Fallon said he hoped people throughout the UK would join together in "remembering those we have lost and recognising the extraordinary courage and dedication of all those who served''.

He said: "They leave a proud legacy - terrorists have been prevented from using Afghanistan as a safe haven for attacks on our streets and it is a safer and more prosperous country.''

The final chapter in the 13-year conflict came last October when the last British troops were airlifted from the sprawling Camp Bastion base in Helmand Province, leaving just a few hundred personnel in advisory, logistical and support roles to help the Afghan army.