Andy McSmith: Thirty years on, will Cameron's speech echo the Iron Lady's?

Tory leader could learn from Thatcher's most famous line

However good David Cameron's conference speech is today, it is unlikely that he will produce a one-liner so sharp that members of his audience will be quoting it 30 years from now.

Yet no one above a certain age who follows politics does not know the phrase delivered by Margaret Thatcher in Brighton, fully 30 years ago: "You turn if you want to – the lady's not for turning."

It was one of those brilliant lines that helped to define a personality.

In October 1980, Mrs Thatcher was the most unpopular prime minister since polling began. Most of the country opposed what she was doing; so did at least half her cabinet. The suspicion had spread that she was too stupid to hear the clamour until, with that one neat phrase, she signalled that she understood perfectly, but she was not giving way.

But the phrase was not hers, and she did not understand it when it was first suggested to her. Its author was an eccentric, elderly thespian named Ronald Millar, who was only vaguely interested in politics.

Leaders now have an army of politicians and professional advisers to draft speeches. Clever though they are, when they reach for a cultural reference they will pick on something topical, popular and obvious – something like X Factor – and the phrases they invent are no better than middling.

Most who heard Thatcher utter her unforgettable phrase knew that they had heard something similar before, but had no idea what. The Lady's Not for Burning was a stage play written in 1948 by Christopher Fry, about an encounter between a soldier who was so sick of a war that he wanted to die, and a witch who wanted to live. It was shown on TV in 1974, which meant that its title still lingered in the memory six years later. Thatcher had not heard of it.

Millar, like Christopher Fry, was one of the generation of dramatists whose work went out of fashion in the late 1950s. By 1980, he was over 60, lived alone with his mother, and never opened his mail because it might contain bad news. He occasionally helped to draft speeches for Thatcher's predecessor, Edward Heath. Surprisingly he survived the change of regime in the Tory party.

"Ronnie got on fantastically well with her," said Sir Tim Bell, then Thatcher's image adviser. "He wasn't thought to be a Heathite. He was a professional entertainer who happened to be a Conservative. A huge number of people would contribute to her speeches. His job was to set the style and tone, and make it appeal to an audience.

"He would show her a draft, she would invariably say 'I can't do this, Ronnie. I don't understand it. It's rubbish.' She would change everything, and then go pretty much back to what he had written."

Thatcher had a legendary inability to understand the best lines fed to her by Millar and others. He once wanted her to make a biblical joke – "And I say to Moses 'Keep taking the tablets'." She told him crossly that people did not say "tablets", they said "pills".

Her final conference speech in 1990 – not written by Millar – contained a long joke at the expense of the Liberal Democrats that was a pastiche of the Monty Python parrot sketch. Before she could deliver it, she had to be given a special viewing of the programme. As a shopkeeper's daughter, she did not find it funny.

But according to Charles Moore, Thatcher's official biographer: "She always had a great respect for people she called wordsmiths. She was at her most difficult about party conference speeches. People who could do good words and could put up with her were very valuable."

Obviously, what David Cameron needs today is an epigram based on an outdated cultural reference. Perhaps as a tribute to Norman Wisdom, who died this week, he could try something on the theme: "Don't laugh at me 'cause I'm a clown". Or maybe not.