Jane Portal, as she was when she worked for Winston Churchill, died last week, aged 93. Lady Williams of Elvel, as she much later became, had an extraordinary life. I encountered her story by chance. In 2015, near us in Sussex, I was told that ‘of course’ (people love saying that when telling you a surprise) Jane Williams’s son, Justin Welby, the Archbishop of Canterbury, was not the offspring of Gavin Welby, as the Archbishop believed, but of Sir Anthony Montague Browne, Churchill’s last private secretary. Of course he wasn’t, I said. I made further inquiries, however, and saw letters and heard testimony which began to persuade me. I also noticed that, when the Archbishop took off his spectacles, he did look remarkably like Montague Browne. I became almost certain that what I had been told was true.

Given that, in good faith, Justin Welby had often talked publicly about Gavin Welby, an alcoholic, gambler and fraudster, as his father, it seemed to me a news story if he had a different paternity. The Churchill connection gave it added interest. As I already knew Justin Welby, I decided to approach him privately and show him my evidence, avoiding ‘the usual channels’. He kindly agreed, and we met alone at Lambeth Palace. The Archbishop had heard the rumour before, he told me, but he did not believe it. ‘Apart from anything else, I am a honeymoon baby,’ he said. It was natural that he thought this, because he was indeed born nine months after his mother skipped her own farewell party at 10 Downing Street in 1955 and eloped with Gavin Welby to marry him in the United States in the face of her parents’ disapproval. But his reaction to my inquiries impressed me with its boldness. ‘Well,’ he said, with a lack of equivocation rare in church leaders, ‘truth is better than doubt, so let’s get a DNA test.’ He worried how his mother might react to the result, however, and thought that if the test proved negative, there would be no need to tell her about the investigation. If it proved positive, he would work out how best to tell her.

I procured a DNA test kit, took it to Lambeth Palace and witnessed the Archbishop taking the test, which resembles brushing one’s teeth. (I already had Sir Anthony’s DNA, though he was quite long dead: his widow had respected his lifelong insistence that she should not clean his hair-brushes.) I gave the sample to the testing company, which sent the Archbishop a rather baldly expressed text: ‘Your Grace, the chances that Sir Anthony Montague Browne is your father are 97.78 per cent.’

The Archbishop took this courageously on the chin, and went with the information to his mother. I do not know what passed between them, but, after digesting the news, Lady Williams, in a statement prepared before we published the story in the Daily Telegraph, admitted that she had gone to bed with Montague Browne, ‘fuelled by a large amount of alcohol on both sides’, probably the night before she fled with Gavin Welby. She said the news had been ‘an almost unbelievable shock’, but admitted that she had at that time had a drink problem. It later developed into ‘serious alcoholism’ which she finally shook off only in 1968. (This explained a fact which had previously puzzled me: why had the unreliable and drunken Gavin Welby managed to get custody of Justin in the couple’s divorce in the late 1950s? The answer was that his lawyers were fiercer than Jane’s and convinced the court that she, because of her drinking, was the worse parent. Perhaps, at that time, courts punished drunk women more than drunk men.) Since 1975, she said, thanks to her marriage to her ‘beloved husband’ Charles Williams, ‘I have been able to blossom as never before’.

This was true. Jane Williams served on the Parole Board and became a prison visitor, magistrate and a deputy lieutenant of London. She tended the Churchill flame and was secretary of the Other Club, which he had founded with F.E. Smith. She was so proud, she said, of Justin, who had emerged ‘from an almost impossible childhood’ to marry his ‘beautiful wife Caroline’ and produce a large family. ‘None of this would have been possible without our firm Christian faith and a determination never to relinquish hope.’ Modestly, her statement never mentioned that her son had become Archbishop. She merely spoke of his ‘position in public life’ as being the reason the story should appear at all. But it was indeed remarkable that he survived so well such a complicated early life.

Given the Archbishop’s agreement, I did not have qualms about publishing the story. He wrote me a generous letter about it afterwards. But I did worry about what Lady Williams might have felt. About 18 months later, I was invited to 10 Downing Street, where she had worked with Montague Browne, to hear her talk about life with Churchill. It was the most charming account of a very young woman’s encounters with an old, eccentric and great man, and that funny way the old have of seeming hardly to notice the young while gradually becoming very fond of them. Robert Armstrong, the former cabinet secretary, was present. He told me that Jane came to matter a great deal to Churchill. Rab Butler, her uncle, whom Churchill had regarded coldly since the years of appeasement, trembled with fear before he had to telephone the prime minister about Jane’s elopement, believing he would be blamed.

Before her talk, I said to Lady Williams I was sorry that my story must have been difficult for her. ‘Not difficult,’ she said firmly. ‘It made everything so much better and we are strong as a family.’ Since she had perfect manners, I shall never know whether she was telling me the truth; but I did sense in her a redemptive serenity, as in the hymn: ‘I once was lost, but now I’m found.’