The last time I saw John Mortimer was at Kathy Lette's book launch before Christmas. She had assembled a crowd in the swimming pool basement of a smart London hotel. Male models posed as lifeguards. Cameras roamed over young television celebrities.

At the far end of the pool, Sir John Mortimer, gravely ill and hollow, watched from his wheelchair. I thought of his father's famous line: "I am always angry when I am dying." By contrast, Sir John exuded slightly bewildered goodwill. "Dying is a matter of slapstick and pratfalls," he wrote.

That evening, he was content when his wife, Penny, 20 years his junior and his best friend, returned to his side. Age was negotiable for him. He said that even at the end he felt about 11 years old, until he noticed that his legs were dropping off.

A year earlier, I had interviewed him in response to a very good biography by Valerie Grove. "What's her name, Verity? Severity?" he asked, loftiness being his favoured form of attack.

John's struggle in his last years was between his work and his health. He desperately wanted to be defined by the former. "My health is the most uninteresting part of my life," he said testily, although he was visibly dying for so long. When I asked if he had planned his funeral he responded: "No, I just carry on working." If he worked, then he lived. Penny said of him with poignant accuracy: "If we were all killed in an accident, John would be desolate but he could still work."

John Mortimer stood for many things. He was unashamedly a champagne socialist and a libertarian. Neither quality is fashionable at the moment. He was a part of Merry England before the dawn of the New Puritanism. His politics were disaffected Labour, but he had more in common with Boris Johnson or, for that matter, with Prince Harry. Being good-natured counted for more than correctness.

He did not care for God, because God was on the side of "Verity, Severity". He told me: "I just believe if there were a God he would be so unpleasant... the sort of person who thinks, 'I haven't much on this afternoon, shall I have a tidal wave?'"

John Mortimer thought that almost anything could be solved by kindness and humour.

His thesis was sorely tested after a difficult first marriage and the recent unexpected appearance of a 42-year-old son. Yet John responded typically by being thankful that a scurrilous unauthorised biography had thrown up the revelation of a loved son. He turned it into an argument against privacy laws.

It is generally true of people who avoid unpleasantness that the tension and misery does not disappear but settles on those around them. Yet John's philosophy of avoidance seemed to produce children of extraordinary sweetness and mettle. His daughter Emily said with dry indulgence: "I wish I had his capacity to breeze through without self-recrimination."

John attributed the success of his second marriage to the fact that "Penny wasn't dramatising and didn't write books". She is also very funny and rather brave. Their younger daughter, Rosie, is a journalist colleague of mine and I can see in her John's perception and shyness – a beguiling mix in a journalist – and Penny's strength of character.

John Mortimer's brand of not-as-gentle-as-you-think humorous writing was too mild to be feted by the critics, but it was a cry for lost England, for humanity and good sense, and his beloved Magna Carta.

Sarah Sands is editor-in-chief of British 'Reader's Digest'