POST-mortems were carried out on both children which involved expert advice from Great Ormond Street Hospital in London.

Dr Darren Fowler, a consultant paediatric pathologist based at Southampton General Hospital, examined Jayden’s body and organs while Bradley’s was carried out by Home Office pathologist Dr Hugh White.

Both experts were unable to come up with a cause of death.

Dr Fowler said numerous investigations were carried out into viruses and bacteria, including chicken pox which Jayden was thought to have in the days before he died.

However he told the inquest that children “don’t usually die” from chicken pox and the Health Protection Agency figures showed that any child that did would normally have a serious underlying health condition.

He said there was concern that the brothers had died from a genetic or congenital disease and that was part of the investigation but nothing was found.

Asked specifically to consider smothering by a soft material such as a duvet or pillow, Dr Fowler said it “was not possible to answer that question”.

Dr White told the inquest how Bradley had tiny pinpoint haemorrhages on the left side of his face and two bruises on his head but there were no other signs of injury.

He said that such haemorrhages can be seen in cases of strangulation or smothering, but were also not uncommon in women giving birth or someone suffering a heart attack.

Dr White told the hearing he could not draw any definitive conclusion from their presence but agreed that smothering could leave no mark at all.