He is Jerusalem’s vanishing Englishman. One moment, Dudi Horn is on a building site, instructing a foreman or meeting a client and the next, poof, he has disappeared.

If there is an emergency near him, whether it is a terrorist attack, a baby choking or a pensioner falling over, he makes a dash there. For over a year he has been volunteering with United Hatzalah and receiving updates from its dispatch centre about where he is needed.

“Not long ago I had a meeting on a business deal when a call came through saying a baby is choking. I just ran out of the door,” says Mr Horn, 39, who grew up in Manchester.

“Afterwards, I went back to the client to say sorry, and he said, ‘Why are you apologising? You just saved a baby’s life’.”

He says that Jewish values and British values combine to make him determined to volunteer.

“I feel it’s part of the British identity to always give and help,” he reflects. Even when it takes a toll on his home life, he responds to calls as they come through, causing him to miss family meals and events.

In United Hatzalah’s dispatch centre in central Jerusalem, staffer Raphael Poch stands in a control room covered with screens monitoring emergencies all over the country.

In this room, Jewish and Arab employees work together to get treatment provided as quickly as possible. A disproportionate number of volunteers, he notes, are immigrants who arrive in Israel with an idealistic desire to help others.

“The level of self-sacrifice that our volunteers show on a regular basis is often far greater than what anyone expects of them,” he said. One of the fundraising videos he helped to produce cast a volunteer as a superhero who works in a normal job by day and saves lives by night.

Some of the most traumatic calls for volunteers are terror scenes.

“It was very tough to get there for the first time, seeing the blood pouring out and having to try to make sure the person is breathing,” Mr Horn recalls. “Then, after a while, you get used to this and in a way that’s more difficult.”

Londoner Shmuel Stern, who has clocked up 5,000 calls over a decade of service, said that the terror scenes, where he has held “many” dead people, are not the hardest for him.

Tough as they are, his faith tells him that “terror victims are sacred ones who go to highest place in heaven”, but he finds it particularly hard to go to homes where life is about to change forever.

“What scares me is going into a home where a child is convulsing, and the parents are about to discover a condition like epilepsy which will need medication for the rest of the child’s life.”

Mr Stern was prompted to train as a Hatzalah medic after a couple of medical emergencies with his five children, during which he was unable to give first aid. Since then he has given CPR on countless occasions, and delivered 45 babies — all during moments snatched from his studies in kollel or work in property, depending on the day.

Every Hatzalah volunteer has their own tricks for keeping their sanity — especially in cases where lifesaving attempts do not work out — and Mr Stern’s is generally to not look at the faces of patients.

“In CPR you can either look at the face or not, but I choose not to look at the face because that kind of thing probably wouldn’t leave me. Then, it’s hard to forget, and that’s the stuff that nightmares are made of.”

Popular culture, he notes, creates warped expectations of what emergency medicine is like.

“There are few happy endings,” he says. “But on TV, 100 per cent of CPR patients are brought back to life.”

When there are happy endings, the patients sometimes stay in contact. When he spoke to the JC, a man in his fifties whose life he had saved seven years ago had just called from America, where he now lives.

“He just called me up last night and said thanks so much for saving my life,” Mr Stern recalls.

“I was in the middle of shopping when he collapsed, and I had lots of kugels in my hand, and had to think whether to take the call or finish shopping.”

Hatzalah volunteers rush to help Arabs and Jews alike, and Mr Horn says that when he goes to Palestinian homes in Jerusalem it “cuts the hatred out, just from the fact people know we’d never turn a blind eye.” For him, whoever is in need, answering the call is a mitzvah.

“During the Shabbat meal two weeks ago I went out twice, once during soup and once during main course. When sitting down to cold soup I said to the family ‘this is the soup of a mitzvah’.”