Charles Cornell suffered serious brain injuries in the accident on the M11 in Essex in 1991 which left him "a more pleasant personality", said Lord Justice Stuart Smith in the Court of Appeal.
But although friends and relatives thought the change was "for the better", his "less aggressive" manner robbed him of his thrusting nature and he was described as "unemployable" in a "reputable sales force".
He had been awarded pounds 156,143 damages by a High Court judge in January 1996.
But because the defendant had paid pounds 175,000 into court to settle the case, Mr Cornell would have ended with nothing because he faced paying all the legal bills under court rules.
Three appeal judges increased his award after finding that he should have been given pounds 220,000 for future loss of earnings which took into account the problems he faced in finding jobs.
The judges had heard that a clinical psychologist, Dr Graham Powell, who examined Mr Cornell, of south-west London, found that he was now only capable of "muddling through life" and his future employment prospects were "very uncertain indeed".
Mr Cornell, 31, was injured when a car being driven by his insurance business partner, Robert Green, left the motorway and ploughed into a field.
He suffered multiple injuries, including damage to the frontal lobes of his brain which impaired his IQ, caused intermittent memory loss and lowered his ability to concentrate.
The judges cut his award for injury, pain and suffering from pounds 87,500 to pounds 60,000, but increased the pounds 30,000 he was awarded for future loss of earnings.
Lord Justice Stuart Smith said Mr Cornell - an Old Harrovian who gained two A-levels when he was 16 - had been described as "bumping along at the bottom of the market" since the accident and was now unemployed.
He had lost the aggression, concentration and thrusting nature necessary for a successful insurance salesman and could no longer compete in the market place. His skills had been lost at the outset of a career which had looked bright. He had been voted one of the most successful salesmen in the insurance market with "flair, stamina and a capacity for hard work".
The judge said the accident had taken away his "competitive edge" and he often fell asleep in the afternoons - a situation "few employers would tolerate".Reuse content