A paramedic who lied about his failure to try to revive a collapsed heart attack victim on a 999 call was jailed for a year today.

Barry Baker, 59, who collapsed and died after making a 999 call. Photograph: PA

Karl Harris, 45, tried to involve a trainee colleague in his deception after telling him "not to bother" to give first aid to Barry Baker, 59, who weighed 30 stone.

The father of two was told by a judge that his actions struck at the "roots of justice and the trust people have in the ambulance service".

He was sentenced immediately after a jury rejected his not guilty plea to a charge of perverting the course of justice, following four hours' deliberation at Lewes crown court.

The trial was told that Harris, a former soldier who served with the Parachute Regiment in Northern Ireland, had been called out from his base in Brighton when Baker rang at 4.14am in November 2008. The phone was left on and the court heard Baker's laboured breathing before the ambulance arrived six minutes later.

Harris and trainee Ben Stokes, 35, could then be heard talking briefly before there was a loud thump, which the jury was told was Baker slumping to the ground. Harris's comments to Stokes could not be made out, but Richard Barton, prosecuting, said that he told the younger man: "He's dead. There's no point. I've seen this before. It's not a viable resuscitation. Don't bother."

A second tape played to the jury recorded Harris's call to police, when he claimed that Baker had collapsed before the ambulance arrived, and that his body was wedged in an alcove surrounded by clutter. He told police that the house was "in a right old state" and ended: "There's not a lot we can do, really."

Harris then filled in forms falsely and continued to tell his 35-year-old colleague what to do. Giving evidence, Stokes, who had not previously worked with Harris, said that he felt "sick" when he was told not to bother with Baker and to join in the lie about finding him already collapsed.

Ambulance regulations require "vigorous resuscitation attempts" for around 20 minutes "whenever there is a chance of survival, however remote". The crown accepted that Baker would not have survived and did not hold Harris responsible for his death.

Harris told the jury that his eight years experience as a paramedic led him to the honest belief that Baker was dead. The single man had lived alone since his parents' death in the mid-1970s and had become obese after a hip operation left him on crutches.

Although he worked in Brighton jobcentre for 42 years, he seldom invited anyone home and his house had fallen into disrepair. Harris said that it would have been physically impossible to resuscitate him anyway, because of his size and the chaos of household possessions in which he lay.

He told the jury that the house had a smell which "made you choke as you walked through the door," although he added that the state of a patient's home would never make a difference to the way he did his job. He said that Stokes had gone into the house first and Baker might have collapsed before he followed him in.

Harris, of Portslade, East Sussex, stood expressionless as the sentence was passed by Judge Guy Anthony, who told him that he committed "a gross breach of trust through a clear and deliberate decision to lie". The judge said: "Quite why will perhaps only be known for certain by you. Perhaps you felt there was more you could have done and you simply did not want to have the hassle of having to fill in large numbers of forms and explain why you did not or could not do more than you did."

Gillian Jones, in mitigation, said that Harris had no previous convictions or complaints against him. He knew that his actions were "silly and stupid things to have done".

After the verdict, James Pavey, of the South East Coast ambulance service, said that an internal investigation would rule on the future of Harris, who has been suspended since a colleague raised concerns about the incident. Stokes was not charged but has been placed on restricted duties.

Pavey said: "The standard of care that has been reported during this trial is not reflective of the dedication and commitment of our staff, who come to work each day to care for the patients that need our help. Our highest priority is to provide a safe, responsive and high quality service to our patients."