Four members of the same family are ticking time bombs - they have a genetic "sudden death" condition that could kill them at any moment. 

Rob Griffiths, 44, and three of his children - Rhys, 20, Rhiann, five and Nelly, two - all suffer from Long QT syndrome, which can cause the heart to stop suddenly. 

Strong emotions and sudden shocks can trigger an attack.  Even the bleeping of an alarm clock could be fatal. 

The family were alerted to the condition four years ago when Rhys, Rob's son from a previous marriage, collapsed while at an adventure training camp. 

Tests revealed Rhys, now a university student, had the hereditary heart condition. 

He had to be fitted with an internal defibrillator which delivers electrical impulses to jolt the heart back into a normal rhythm.  Rob and Rhiann were also tested and confirmed as having Long QT.  Nelly was diagnosed at birth. 

Rob, from North Wotton, Norfolk, said: "What happens is the heart can end up short circuiting and completely shutting down.  It's like a power cut of the electrical supply to the heart." 

Rob, a logistics manager, served 20 years in the Army and was amazed to discover he could have keeled over at any time. 

He said: "I have been in operations in Bosnia and Northern Ireland carrying heavy guns and packs, but I've always been fine. 

"It just goes to show you can't let this rule your life.  Some people have cancer and they're a lot worse off than us." 

Rob and his wife Jan, 43, said their priority was to make life as normal as possible for brave little Rhiann and Nelly.  He said: "You can't wrap them in cotton wool.  That's not the life we want them to have.  Rhiann tells everyone she ha s special heart." 

Jan said her family's condition was a constant worry but she had learned to cope. 

She said: "It was pretty scary when I first found out about the girls having Long QT.  It was bad enough having Rob confirmed. 

"It was such a shock to the system, especially as nobody knows much about it." 

Jan said before Nelly was born it was difficult to decide whether to have another baby. 

"Eventually we decided it would be wonderful for Rhiann to have a brother or sister," she said. 

Last month Rob and Rhiann completed a five-mile walk across eight London bridges to raise £400 for the charity Cardiac Risk in the Young (CRY). 

The family have been grateful for the help of CRY, which is campaigning to raise awareness of the condition and other cardiac abnormalities.