In hope, in fear and in mourning, the families wait by the telephone

It's just a case of hoping, one of the British relatives said. Hope is tenacious but it is starting to fade now for the families of more than 100 Britons believed to have been working in the twin towers of the World Trade Centre on Tuesday morning.

Across the UK, relatives have not only been glued to television sets like the rest of us but maintaining an unbroken vigil by the telephone. And, although no British bodies have yet been found, for the Merseyside relatives of Ron Gilligan, who was working on the 103rd floor of the north tower, for the Sheffield family of Nigel Thompson, working on the 105th, for the Dundee relations of Derek Sword on the south tower's 89th floor, and for many, many more, the silence of the past three days is increasingly coming to mean only one thing.

Eric Redheffer, whose wife Sarah, 35, from London, was helping the UK-based Risk Waters Group host a financial technology conference in the Windows on the World restaurant on the 106th floor of the north tower expressed yesterday what all must be feeling. "If you go to a church," he said, "light a candle for us."

The accurate British death toll in New York's tragedy is still unknown but, yesterday, Jack Straw, the Home Secretary, said it might eventually reach "the middle hundreds." Should it do so, it will not only be the greatest number of British casualties in a terrorist attack, but maybe the biggest British peacetime death toll for nearly a century, surpassing the 188 people killed in the Herald of Free Enterprise ferry disaster in 1987, and the 167 dead in the Piper Alpha North Sea oil platform explosion in the same year.

The people trying to put the grim list together are the Consular Department of the Foreign Office, who have created a database with three categories: people positively known to have been in the World Trade Centre, people probably there, and people possibly in the complex. All Britons who were there and who got out safely are being asked to ring the British consulate in New York, and the two lists are being matched up.

So far, more than 12,000 people have rung the Foreign Office help line in London asking for information about family or friends in New York, and it is from these calls that the initial Government estimates of casualties are being made.

But, although no official list is being released, names are seeping out in local communities across the land. In Sheffield, they are grieving for Nigel Thompson, 33, who worked for bond traders Cantor Fitzgerald, who was actually on the phone to his twin brother Neil, employed by another New York broker, when the first plane crashed into the north tower opposite him. He was cut off shortly afterwards and nothing has been heard since.

The twins had been inseparable through students days, reading economics at York University, before moving to careers in the City and on the trading floors of New York. Since their firms traded together, they spoke by telephone every day. Mark, the twins' elder brother, said "Nigel said 'We are under attack. We are being evacuated' and then they got cut off."

Mr Thompson said it would be a miracle if Nigel, who was due to celebrate his first wedding anniversary in October with his New Yorker wife Rosanna, were found alive after the attack. "He is still classed as missing but because he works on the 105th floor and because no names have been coming out of Cantor Fitzgerald as survivors, we are bracing ourselves for the inevitable," he said. "We are expecting his body to be found today.

Mr Thompson's parents, Norman and Patricia, privately fear the worst. But Mr Thompson Snr, a retired Sheffield police and coroner's officer, said: "Nigel is so fit. If anyone is capable of getting out, then he is. He was such a gentle lad. He was likely to stop and help people rather than get out himself." The family are hoping to fly to New York next Tuesday to try to comfort Neil and Rosanna.

Also working for Cantor Fitzgerald more than 1,200 feet up in the south tower – above where the second jet impacted – was Ron Gilligan, who came from Liverpool. Nobody has heard from him since he left his British wife Elizabeth and their children Ashley, 16, Ainslie, eight, and six-year-old Dherran, on Tuesday morning, and set off for a day at work.

When news of the attacks filtered through, Mr Gilligan's family, still living in Merseyside, immediately rang his office - but could not get a reply.

"You have to be optimistic, you can't let yourself think the worst," said his elder brother Les, who lives in the Liverpool suburb of Childwall, yesterday. "We've rung the hospitals and he isn't there. We have rung Cantor Fitzgerald and, so far, he isn't one of the survivors. What can you do except hope and pray that he is, dear God, still alive? But you look at the pictures and you watch the television and you just think ... jeez. I just hope that, as the plane went through the building, Ronnie went instantly. I hope he didn't suffer."

Les Gilligan and his sister Anita plan to fly to New York as soon as air services are resumed to be with Elizabeth. Their sister-in-law, Brenda Portman, will also travel out. She said she had telephoned her sister countlessly since Tuesday. "We are devastated. Shattered. There aren't any words to say how we are feeling at the moment," she said. "We haven't slept since we heard that the World Trade Centre had been hit. We just keep watching the news. Liz hasn't watched the television. She is beside herself with the sheer enormity of it all. The children know and are taking it in. But how do you tell an eight-year-old and a six-year-old what has happened? "

Keeping the telephone vigil in Dundee are the parents of 29-year-old banker Derek Sword, who worked on the south tower's 89th floor for the American finance firm Keefe, Bruyette & Woods. David and Irene Sword are still hopeful their son might be alive, but again, have heard nothing.

"The first we knew was when Derek rang to say he was fine and told us not to worry. That must have been seconds after the plane went in," Mrs Sword said. "That was really it, and we have not heard anything else since. We have been watching the television and checking with the Foreign Office but there is no news of him yet. It is so, so difficult for us. We feel helpless and are just hoping that he is safe and well.

"His fiancée has told us that there are hundreds of unidentified people in hospitals over there and we are praying that our son is among them. Until we hear otherwise, we will go on believing he is okay. But this is just the most harrowing thing and is truly awful."

The family said they feared they might have to wait days before they have confirmation about what has happened.

Mrs Sword added: "This is just something you never, ever imagine that you would have to go through. This waiting about just destroys you, But you have to be positive and that is what we are all trying to do. The fact that Derek phoned us has given us hope and, for his sake, we will not give up for anything.

"We also hope that his fiancée over there will be able to get information quicker than we can over here."

Maureen Sullivan, 30, a pharmacist who got engaged to Mr Sword just 10 days ago, described from her Manhattan home yesterday how he had phoned her twice, first contacting her in the moments after the attack.

"He phoned me after the first plane hit the other building – he was in tower two," she said. "He phoned me to say it wasn't his building and that he was okay. Then, after the second plane hit, he phoned me again to tell me that his building was now on fire, but he was okay, to call his parents to make sure they know he's okay, and that he was going to be evacuated."

Ms Sullivan said she had been calling his mobile phone regularly since the tragedy, but it was not ringing. She said: "I call it every hour just ... you know ... I call his cell phone all the time, but it just forwards me to a voicemail, it doesn't ring."

Asked how she was coping, she responded: "Just, you know, holding in there."

She added: "We've been in constant touch with his family and his brother in Dubai. Everybody has been ringing the doorbell and phoning up to offer support. When I can't stand sitting around any more I go out hanging flyers everywhere with his photo. I call the hospitals constantly. It's just a case of hoping."