Rosebery has faded from public memory, but Winston Churchill will always be remembered as an orator, thanks to his immortal performances in 1940. Yet, as David Cannadine reminds us in his introduction to a collection of Churchill's speeches, this mastery was only attained as a result of very hard work: "He studied — and often memorised — the greatest orations of Cromwell, Chatham, Burke, Pitt, Macaulay, Bright, Disraeli and Gladstone . . . He laboured heroically to overcome his lisp and his stammer . . . Above all, he was obliged to lavish hours on the detailed construction of the speeches themselves."

It would be astonishing to find a politician today who devotes so much energy to writing speeches. Few understand what a valuable use of time this would be. To write a good speech is to be forced to clarify what you think about something. You have to decide how you are going to justify your opinions, and also how you are going to hold a particular audience. You end by discovering how to be yourself.

To deliver a bad speech — one which is more obscure or banal or dull than it would be if you had taken trouble over it — is an insult to your audience. To her credit, Margaret Thatcher took a great deal of trouble with her speeches. Even her enemies could not deny her seriousness of purpose. She conveyed a determination to be straight with people which is seldom found in her successors. Ferdinand Mount has given, in his memoir Cold Cream, a very funny account of the horrors of writing speeches for her: "Her ear was unfailingly tinny and, though she could be devastating and inspiring in unscripted harangues, the sight of a written text would make her freeze."

In 1983-84, during brief service in the Conservative Research Department, I found myself recruited as the junior member of a team preparing a speech for the Prime Minister to deliver about foreign policy. It was Oliver Letwin's idea to write this speech, and he sat typing it at an early word processor which he alone knew how to use. I stood behind him making suggestions, alongside Alistair Cooke, a historian who served for many years as the research department's deputy director and as the marvellously eloquent and exacting editor of its publications. He has recently been ennobled as Lord Lexden.

We began by announcing that there were three fundamental principles of British foreign policy. After a while we thought of another principle, so changed this to four fundamental principles. I was delighted when my colleagues agreed to include in the peroration the well-known but perhaps slightly unexpected quotation by Oliver Cromwell about "a plain russet-coated captain that knows what he fights for, and loves what he knows".

The speech was put in to Mrs Thatcher, who was said to approve of it. We waited to see if she would deliver it. It was reported that she kept our speech in her handbag, and would produce it during difficult speech-writing sessions with the words: "I think there might be something here that can help us."