Susanna Pell is taking the day off work tomorrow and planning a smart lunch in the West End of London with her mother Jan and brother Geoff – she is hoping for a table at the Wolseley, one of the capital’s most fashionable restaurants. On the last two anniversaries of 7/7 she has laid flowers at Edgware Road Tube station. “But I don’t want the day to be dominated by the bombing for the rest of my life,” she says. “It happened and I feel I have to mark it, but I want to redefine the focus of the day, make it into a sort of official birthday, a day to give thanks for being alive.”

On the morning of July 7, 2005, Pell, 27, had just boarded the Circle line train leaving Edgware Road and had seated herself in the first carriage when Mohammad Sidique Khan detonated his suicide bomb. She was knocked unconscious by the blast and came round to find herself in darkness. “It was pitch black and I couldn’t breathe,” she says. “The smoke was so thick and full of grit, like the dust from a demolition site. I was dizzy and struggling to stay conscious. I assumed we’d crashed. For a few moments there was silence.”

Pell was smartly dressed and in high-heeled shoes. She had been working at Christie’s, the auctioneers, after a postgraduate degree in the history of art, but was hoping to break into fine art insurance. On 7/7 she was supposed to be starting two days’ work experience with a City broker and had arranged to get her hair done at a hairdresser’s in Kensington on the way.

Instead she found herself trapped in a hot, dark, smoky hell of tangled metal. She did not know it yet but a few feet from her, in the second carriage, seven people – including Sidique Khan – lay dead. From the next door carriage came screams and shouts of “Help, we need help”.

A fellow passenger, Chris, asked if anyone knew any first aid. Pell, the daughter of two doctors, although she had no medical training herself, stepped forward to help. “It was just instinctive,” she says. “The people in the next door carriage were in trouble and we had to see if we could do something for them.”

The door between the carriages, next to where she had been sitting, had been blown away and she climbed gingerly through the gap, her ears ringing with tinnitus caused by the explosion, blood running down her face from a head wound and her face and head studded with fragments of glass.

“In front of me was a pile of mangled metal, debris, luggage and a mound of bodies. It was dark and the ceiling had caved in. I saw a dead woman on the floor whose clothes had been blown off, other than her white knickers. I looked to my right and saw a guy whose leg was horribly twisted and broken and bleeding badly.

“I later found out his name was Matt. Next to him was a woman called Alison, who was just staring into space. It felt very weird, everyone was covered in ash and soot, so it was this dark grey face with staring white eyes. I assumed she was dead, but I later found out she had a punctured lung.

“I tried to reassure Matt and calm him down. His leg had been ripped to shreds and was bleeding so badly that I knew I had to elevate it. I said to him, ‘This is going to hurt’, and I untwisted it and lifted it over to rest on Alison’s lap. I was wearing a cream pashmina which I took off and tied round the top of his leg as a tourniquet. I met him later at a memorial service and he had no memory of any of it. It was strange when to me it is still so vivid.”

She then helped Danny, a builder, and his friend, who had been sitting opposite Matt. They had both lost their hearing as the blast had burst their eardums. Someone from the first carriage shouted that it was possible to get out onto the tracks. So she and Chris took Danny and his friend by the arm and slowly led them over the rubble. “They were in shock and because their ears were damaged their balance had gone,” she says. “We had to half-carry, half-drag them to get them out.”

It was only an hour or so later, when they were led up from the tracks and out into the daylight, that she cracked: “I just burst into tears. It was as if I suddenly realised the enormity of what I’d been involved in.”

For 18 months she could not face using the Tube. “I would panic, even on buses,” she says. “It wasn’t a case of flashbacks, I’d imagine all sorts of new and horrific scenarios. I’d feel a bomb was about to go off and imagine all the people around me injured and covered in blood. I’d find myself on a bus with tears running down my face.”

She finally admitted to herself that she needed help and had counselling. A fellow passenger who had been on the bombed train went with her on her first trip on the Circle line: as the train passed through Edgware Road they held hands.

Susanna’s story will be part of 7/7: The Angels of Edgware Road on Channel 4 next Sunday at 7pm

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