Sussex detective constable Clinton Novelle is well used to dealing with tragedy.

As a trained family liaison officer with Sussex Police, he counsels families of the victims of murder, rape and road crashes.

But nothing was to prepare him for the scale and depth of emotion he was to encounter in New York - families scouring the streets for news of their missing loved ones, makeshift shrines at every turn and the smell of death and destruction wafting over the city.

People walk the streets wearing masks to shield them from the stench of rotting bodies.

As he greeted the families of British victims, Mr Novelle struggled to maintain a composed exterior in the face of such overbearing sorrow.

Walking round the city, he said: "It is the families of the victims who are left to suffer. It is heartbreaking to have to go to a victim's house with the family and feel the pain they are going through.

"Relatives from the same family showed a whole spectrum of emotions within a couple of moments. They ranged from total acceptance to total confusion. Some would remember all the good times and others were unable to even comprehend what had happened."

Given less than 24 hours' notice that he would be sent to New York on the Sunday after the tragedy, he found himself in a country gripped with fear.

Before witnessing the apocalyptic scene of the collapsed World Trade Centre, he and the team were taken to Union Square, the focal point of the grief.

Mr Novelle, 42, a father of two based at Haywards Heath, said: "We walked into a wall of emotion. I just stood there and observed people crying and comforting each other. Others walked round in a daze.

"There were flowers, poems and American flags everywhere. At that point, families still had hope victims would be found alive and put up posters with detailed descriptions of their loved ones.

"I felt their pain, horror, anger and despair as I realised every bit of paper was a real person. It dawned on us the enormity of what we would be dealing with."

The team had to provide both practical assistance, such as collecting every British family member from the airport, and emotional support.

As we walked around the bleak ruins of the centre, the rubble still smoking, Mr Novelle said the first thing most of the families wanted to do was get close to Ground Zero.

Yet this was a crime scene, with recovery staff working away day and night in their grim search.

Instead, families were forced to say their final goodbyes at nearby shrines such as Our Lady of the Rosary Church, set up specifically for British relatives.

Mr Novelle said: "Most of them are denied even the privilege of being able to say goodbye to their loved ones at a funeral. As time goes by, they know many of the victims will never be found. At least now the city authorities have agreed to issue death certificates which should be valid in the UK."

We paused to look at tattered photos of missing victims, attached to lamp posts, bus stops and dust-filled shop windows.

Mr Novelle said many of the British victims were highly successful men in their late 20s or early 30s who had married Americans and made a life for themselves in New York.

He said: "One of the most moving experiences was when I visited a missing British man's home in New Jersey with his family who had just flown over. He had an American wife and on September 11, the day of the attacks, his only son was just 13 days old.

"I was struck by how many family photos there were all over the house, including one of the father holding his son. I couldn't help but ask why. There was a baby who, through no fault of his own, would have to suffer for the rest of his life. His mother would have to explain his father was an innocent victim."

He spoke of another missing British man who never got to celebrate his year wedding anniversary with his American wife on September 30.

He said: "We had to go to homes with families and pick up victims' personal belongings. One mother had never been out of the UK before and didn't have a passport. We got in contact with the British Consulate and managed to get her one. She would not have been able to come here otherwise."

In his efforts to support the victims' families, he experienced a common empathy with officers and firefighters in New York who were still struggling to come to terms with their own loss.

Hundreds of firefighters died in the attacks as they tried to rescue victims from the twin towers.

Mr Novelle and I went to talk to one firefighter who lost ten colleagues in the tragedy.

Captain Mark Munnelly, of the 17th precinct brigade in East 51st Street, Manhattan, told us: "It was total chaos. We knew some of our guys had gone down to the centre but we kept hearing different rumours of sightings and phone calls.

"One firefighter had called his wife to tell her he was okay but then we heard nothing. We soon realised both the Ladder Two rig and its men were missing. To lose ten guys out of 14 was beyond comprehension. I will take the pain with me for the rest of my life."

On firefighters being hailed heroes, he said: "The guys who were killed showed true courage and dedication. No one thought the towers would collapse but they knew the dangers and still kept going in.

"Yet we are just regular guys. We don't do our job for the glory but because we want to help people. We will continue to do this as best we can."

Mr Novelle said one of the images that made the most impact was four firefighters carrying the body of Father Mychal Judge, chaplain of the New York Fire Department, who was killed when the towers collapsed.

He said: "To see four powerful men carrying their chaplain as if he was a baby was incredibly moving. You could see the pain etched on their faces. People like the chaplain knew the risk and paid the ultimate price."

The magnitude of the events was hammered home to him at a memorial service for British victims held at St Thomas Church in New York on September 20.

He said: "I looked around and saw families crying alongside Tony and Cherie Blair and Bill Clinton. It meant a lot that such powerful people gave their solidarity."

He paid tribute to the support from the British Consulate and charity Cruse, which offered counselling to them and the British families. Yet he admitted what got him through the aftermath of the attacks was his own team with officers from the Metropolitan Police, Thames Valley, Surrey, Kent, Essex, Hampshire, Dorset and North Wales.

With tears in his eyes, he said: "We came here as strangers and will go away with an experience no one else but us can ever understand. We lived with each other, worked together and have become very close. I never felt alone or like I couldn't cope. Our motto was unity.

"I am looking forward to getting back to normality but it will hurt when I have to say goodbye. Every one of the team will always be in my soul.

"I am so proud of what we achieved. We did not do it for praise or glory but because we cared and wanted to help. We will do so for as long as we are needed."

Mr Novelle returned to Sussex on Tuesday.