ES News email The latest headlines in your inbox twice a day Monday - Friday plus breaking news updates Enter your email address Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid You already have an account. Please log in Register with your social account or click here to log in I would like to receive lunchtime headlines Monday - Friday plus breaking news alerts, by email Update newsletter preferences

More than 1,000 police and soldiers - including SAS troops - staged a mass exercise today to test their ability to respond to a Tunisian-style gun attack on London.

Elite police firearms units, the military and Government officials responded to a series of rolling mock attacks on locations across the capital.

The exercise - codenamed Strong Tower - came as tributes were paid to a Londoner killed in the Tunisia beach massacre.

Chris Dyer, 35, who was on holiday with his wife of two years Gina Van Dort, 32, when gunman Seifeddine Rezgui unleashed a deadly machine gun assault on sunbathers.

Today friends and neighbours of Mr Dyer today paid tribute to the electrical engineer, who was originally from Ruislip, west London.

Mr Dyer’s wife, who refused to let go of his body despite being seriously injured, was one of four Britons airlifted to the UK yesterday by the RAF.

A friend said: “They are really lovely people we are in total shock. Chris and Gina knew everyone around here and we are all Facebook friends it is a tragedy. They were always a very close, hardworking couple it seemed. We would not be surprised that she did not want to let him go and clung to him after he was shot.”

The couple, who lived in Watford, had been married for two years and were in the second week of their holiday.

Dr Hajer Kraiem, one of the first doctors on the scene, told how the injured woman at first refused to be parted from her husband.

She said: “When we tried to bring her to the ambulance she held tighter.

“She was hugging her husband. She had major trauma. She was conscious but she couldn’t speak. She’s lucky to be alive.”

Mrs Van Dort, who needs reconstructive surgery, lost an eye after a bullet passed through her chin and out of her face.

There were mounting fears today for another London couple feared to be among the victims.

The grandchildren of John and Janet Stocker, from Morden, had launched a Twitter campaign to find the pair.

The couple, aged 74 and 63, have not been heard of since the atrocity last Friday and family members have since flown to Tunisia in a grim search for the truth.

The police exercise in London was taking place today around the disused Aldwych Tube station and the public was advised that any gunshots or explosions heard in the area were not real.

Just before 11am, piercingly loud, repetitive bangs from blasts and automatic guns could be heard.

Security officials fear a “marauding” terror attack involving multiple gunmen is the most likely threat faced by Londoners.

Scotland Yard has given extra training to front line armed response officers and a specialist counter terror firearms unit is trained to respond to such an incident.

Today Scotland Yard chief Sir Bernard Hogan-Howe said: “The reason we have exercises like today is because, obviously, we are concerned there are people planning terrorist events. We intend first of all to stop them from getting to attack. But should we not stop the terrorists in their planning, it’s essential we disrupt them in any of the attacks that may take place.

“With events like today we are committing around 1,000 people to exercise our plans and make sure that should the worst happen we are ready. And we will be.”

Today’s exercise draws on tactics seen in the terror attack on Mumbai in 2008, the stabbing of two police officers in Australia last year and the Charlie Hebdo attacks in Paris in January

David Cameron has announce a minute’s silence on Friday in memory of the 38 who died when the 23-year-old gunman opened fire in the tourist resort of Sousse.

As the Tunisian authorities arrested 10 people in connection with the attack, some of the survivors claimed there was more than one gunman.

Three Britons have spoken of how they saw a second gunman armed with an assault rifle but dressed differently from Rezgui.

Meanwhile possible connections to extremism in the UK have emerged.

The gunman was linked to Saifallah Ben Hassine, a fanatic who was based in London for at least three years and a disciple of the cleric Abu Qatada, the Daily Mail reported today.

Today it also emerged how Rezgui was finally shot dead by two harbour guards who had raced to the beach in a launch from the local port.

They followed the gunman as he walked up a side street. In testimony quoted by the Telegraph one of the guards said : “He seemed to be under the effects of drugs. He was not afraid to die.

“There was a very big security failure because he was killing for a long time.”

The guard, who did not want to be named, said Rezgui was still carrying an unused grenade and two ammunition clips for his Kalashnikov.

The Tunisian authorities today announced that a thousand armed police officers would be deployed to patrol the country’s beaches.

The announcement came after Home Secretary Theresa May visited the scene of the slaughter yesterday.

The four survivors airlifted to Britain by the RAF yesterday also included Allison Heathcote, 48, who is in an induced coma after also being shot in the arm and stomach.

She had been on holiday with her husband Philip, 53, to celebrate their 30th wedding anniversary today. He is missing, believed dead.

Downing Street said all British nationals injured would be returned within the next 24 hours.