A cancer sufferer allegedly murdered by his family GP would have died regardless of any morphine overdose administered by the doctor, a court heard today.

Dr Howard Martin faces three charges of murder in relation to the deaths of three patients in County Durham, dating back to 2003.

The 71-year-old has denied the charges, despite prosecution claims, that he injected them with large amounts of morphine ''to help them on their way''.

A jury at Teesside Crown Court has been told that Dr Martin would not be going into the witness box.

The GP, now of Beach Road, Penmaenmawr, Gwynedd, North Wales, is charged with murdering 74-year-old Harry Gittins, of Newton Aycliffe, in January last year, Stanley Wheldon, 74, of Coundon Grange, in March 2003, and Frank Moss, 59, of Eldon, near Bishop Auckland, four days earlier.

The first defence witness, Dr Nathaniel Carey, a Home Office pathologist and independent forensic pathologist told the jury how Mr Moss was terminally ill with cancer and would have died regardless of any alleged large morphine injections.

Dr Carey, who the court heard worked on the London bombings and the Soham murders also added that it would be impossible to gauge what exact levels of morphine had been administered at the time.

Dr Carey, who carried out tests on samples from the body of Mr Moss, told the court: ''Mr Moss was in a dying phase and had a terminal and incurable condition.

''Morphine may have played a part but if he was dying already you cannot even be sure of that.

''One would have to look at a hypothetical situation that it may simply have made him die an hour earlier than he would have died anyway.

''It would not be appropriate to include morphine as a cause of death otherwise we would have to include it for any people that died in a hospice.''

Dr Martin has been accused of administering excessive doses of morphine to the three men, whose bodies were exhumed after a police investigation sparked by family concerns.

Dr Carey added that it would be impossible to determine exact levels in any of the cases.

He added: ''You cannot just grab hold of a level and say it would be a lethal level.

''It is a bad mistake that is being made by some toxicologists to talk about lethal levels.''

Further expert evidence is expected to be called by the defence and the jury has been told that closing statements and summing up speeches should start next Tuesday.