John Cox caused a head-on car crash when his 143mph Mazda Xedos suddenly drifted onto the wrong side of a road.
Retired health visitor Edith Murphy, 64, who was on her way to a garden centre with her family, suffered internal bleeding in the impact. She died later in Trafford General Hospital in Greater Manchester.
Investigations revealed Cox, 55, had only two hours sleep in the past 27 hours and had just returned from a business trip in Spain.
The divorcee had been discussing real estate deals with Spanish estate agents in Alicante, caught a 3am night-flight back to Britain but despite his lack of sleep decided to drive his new fiance home in his £28,000 vehicle.
Witnesses spotted the car - travelling at 35mph - drift onto the wrong side of Manchester Road in Carrington and smash head on into a Seat Ibiza being driven by Mrs Murphy's daughter.
Cox, of Snowdon Avenue, Flixton, later denied falling asleep. He claimed he wasn't tired but "elated" because his long time girlfriend Patricia McGough had just agreed to marry him at the third time of asking.
At Minshull Street Crown Court, Manchester, the property dealer - who runs Manchester-based Juan Grande Ltd - showed no emotion as he was convicted of causing death by dangerous driving after only 90 minutes deliberation.
He was also banned from driving for four years. During the trial, Cox got involved in heated verbal exchanges with prosecuting counsel when called to give evidence.
During cross examination he repeatedly tried to use lawyer speak from the witness box, saying: "I put it to you" when asked to explain his defence.
Cox also called associates from a firm of accountants and solicitors plus the stepdaughter of a senior judge to give character references for him.
Mr William Baker, prosecuting, said the tragedy occurred in July last year after Cox returned from his part-business, part-pleasure trip to Spain.
He had been "on a high" after Ms McGough - who was also on the three day trip - had agreed to marry him.
They had caught a 3am nightflight from Alicante Airport returning to Manchester at 7am, whereupon Cox and Ms McGough got a taxi back to his house.
Cox then drove his fiance back to her home in Runcorn before heading back to Greater Manchester.
Mrs Murphy, from Leicester, was visiting her family in Urmston and at noon was on her way to a garden centre with her daughter Joanne Lightfoot, son-in-law Peter and her granddaughters aged three and two.
She was in the back with the children whilst Joanne was driving and Mr Lightfoot was in the front passenger seat.
Mr Baker said Mrs Lightfoot, who was driving at 35mph, noticed Cox coming the other way in his Mazda and losing control of it as he passed a car boot sale.
"The defendant's car drifted across the road onto the wrong side and carried on travelling towards them without braking", said Mr Baker.
"Mrs Lightfoot braked hard, managing to stop her car, but this defendant was not looking ahead.
"Either he had fallen asleep having slept little from a night flight, or because he was distracted. The collision was so strong it pushed the Seat back two and a half metres."
Cox later told police he had spotted a car boot sale at the side of the road and slowed down and pulled out towards the centre of the road.
He said the next thing he remembered was being helped out of the Mazda. In court he claimed he was told at the roadside that the occupants of the Seat were out of the car and apparently fine although one lady needed treatment.
He said he was "in distress" at the time because he had suffered a swollen nose due to the car airbag blowing up in his face. He also said chest pains he felt made him fear he might be having a minor heart attack.
In passing sentence Judge Brian Carter QC said there were many aggravating features missing from Cox's case such as speed, drink and dangerous driving over a prolonged period.
But he said the fact Cox had run a trial and was convicted did not entitle him to any discount on sentence. The judge said: "I feel I would be failing in my public duty if I did not send you to prison."
In mitigation, defence counsel Mr Michael Leeming said Cox was "a man of positive good character" with a clean driving record for 37 years. He would now have to put his marriage plans on hold.
"Whatever the sentence of the court, it would punish him", added Mr Leeming. "Although it may not be much of a consolation, the defendant proffers his apology to the Lightfoot family."
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