Earlier this year, with the fifth volume behind me, I began to look more closely at the boxes of letters, journals and ephemera kept by Benn while he was growing up from a precocious childhood. At the age of 17, for example, he began to keep a time chart, illustrating how he passed every hour of every day. Five intersecting lines plotted his successes and lapses over the course of six months: purple for 'discussion'; blue for the University Air Squadron; red for 'personal'; green for exercise and a pencil line for work.
He also wrote out a life plan in which, unlike Michael Heseltine, he was too modest to record the age at which he would become Prime Minister but in which he did anticipate becoming an MP at 31. In the event, he was six years younger.
The moral pressure to account for time spent is a familiar part of the radical Nonconformist climate in which Benn grew up; his father had kept similar records, and it is a preoccupation, some might say obsession, that has characterised Benn's life and his daily diary-keeping ever since.
The result has been a voluminous output of diaries, possibly the most detailed of any this century. The diaries of Leo Amery, written between 1929 and 1945, were two million words long - similar in scale to Benn's, but the latter's sheer stamina in maintaining them over a period of 50 years outstrips that of most other politicians.
The first question for all editors of diaries to resolve is this: are diaries a literary form or a historical source? Anyone who has read the Alan Clark diaries will know that his voice is so distinctive that editorial interference in his use of language and idiosyncratic style would only diminish their value. But as a source of specifically political history they are limited to reflections on the last gasp of an (apparently) dying Tory ruling elite.
By contrast, Benn's diaries, with their wealth of detail in and out of government - of meetings, votes, arguments, conversations, decisions - are, and will increasingly be, a rich vein for political historians to mine. But in print, as a factual, chronological recollection of the day's events, they have too little descriptive writing, self-reflection or taste for vitriol and lack the remarkable style and language of his speeches, which are full of allegory, parable and anecdote.
In addition, the practice of dictating to an audio-cassette, without an audience or listener, subtly affects the nature of his diaries and makes them quite different from those which originate as the written word or are dictated to an audience such as a secretary. As editor I had the job of turning this overwhelming bulk and variety of information into volumes of publishable length. The relatively simple task was to make them concise and intelligible to the reader; I decided to excise phrases, full sentences and whole sections of dialogue from a particular entry, without indicating the excisions in the text. It was a convention adopted by the editors of The Shorter Pepys, and to good effect, but it inevitably distorts the balance of the entry concerned.
The larger problem was what to select out of this great verbal stream of consciousness. Richard Crossman is reputed to have said when editing his own diaries for publication, shortly before his death in 1974: 'Let's cut out everything about Fred Willey and the Ministry of Land and Natural Resources - no one will be interested in that]' Selection is at the heart of the editor's job.
When I began to prepare the books for publication, it was the Crossman diaries that were my main inspiration. Janet Morgan had begun working on them in 1970; with Richard Crossman's death four years later she inherited the task of editing two volumes herself. The Crossman diaries set an editorial standard which others following in their wake have tried to emulate. But in my case my integrity as an editor was challenged on occasion, albeit amicably, by the extant diarist himself, who was indeed still an active politician.
Our concepts of what was 'interesting' often differed. The appearance of famous or important men (inevitably) in the pages of a diary is not in itself a guarantee of readability and I was constantly asking, 'Yes, he may be the Queen's Private Secretary, but is what he is saying interesting?' On these occasions we would argue over the significance of an entry and eventually reach a compromise.
What to exclude from the published diaries was a much harder decision than what to keep in. You cannot possibly know what in the long run is going to be historically important or interesting. Tony Benn and I considered the question of cuts together, going through the text separately and then comparing our suggestions. My instinct was, 'Let's cut out foreign trips - no one will be interested in those.'
This proved to be a major disagreement between us throughout my work on the five volumes: my sympathies were all with Patrick Gordon- Walker, the Education Secretary who, at a Paris science conference in 1968, spent his whole time visiting Impressionist paintings or doing the Times crossword. That was, in my view, the most worthwhile part of Benn's entry for that particular day; it might transpire that a discussion that day between Benn and the French Minister of Science about enriched ur-
anium will prove to be of longer-term significance.
The compromise was to reduce the reporting of such trips to a minimum - where I could not exclude them altogether.
At a distance of 10 years, with the benefit of hindsight, certain obvious elements stood out for inclusion. Few in 1978 would have been interested in a discussion in the Cabinet about the European Money System. Certainly not me. But over the next 10 years the Exchange Rate Mechanism came to haunt British political life - indeed, it helped to bring down a Prime Minister - so that the preceding arguments and position taken up then become immediately relevant.
A year earlier a ministerial meeting took place at Number 10 about a little group of islands in the South Atlantic which, it was thought, had some oil lying under them. Should the Government therefore concede to Argentina a 200-mile sovereignty zone? The Labour Defence Secretary pointed out that the Argentine government had ordered pounds 700m worth of warships from Vosper Thorneycroft, so that in the event of a war the Falkland islanders and possibly the British forces would be attacked with British warships - a small but interesting sidelight which, had it not been for the war four years later, would probably have landed up on the cutting-room floor.
I confess that I was not excited by the discussions, especially in Cabinet, of economic or fiscal policy in the unedited diaries - a somewhat serious drawback considering how much time politicians spend trying to get it right. My feeling was that readers would not be riveted by the esoteric arguments or the facts and figures, and therefore large swathes of such detail was cut from the diaries, with the exception of a few events, such as in late 1976 when the International Monetary Fund succeeded in imposing expenditure cuts on the Labour government.
Fortunately for me, there were enough doctors or PhD hopefuls all wanting to go through the original transcript of those eventful months with a fine-tooth comb to ensure that my gingerly attempted editing was accurate to the last dollar.
I decided early on in the editing that the diaries must also reflect life outside Cabinet, Shadow Cabinet or indeed Parliament, so that every volume cuts across a period of Labour both in government and opposition.
The Royal Family was featured in the current Radio 4 series The Benn Tapes (9.45pm today), which used the original cassette recordings of the diaries: surprisingly, it proved to be an ideal medium for the diaries, encapsulating in Benn's sombre tones the seriousness of the occasion, the disagreements between Cabinet members and the final unpalatable outcome. It also had the effect of emphasising the incidental, which might make no impact in print, such as the occasion when Jim Callaghan sang 'I am the man, the very fat man, who waters the workers' beer' at a Durham miners' dinner, an evening chronicled and recorded by Tony Benn.
I suspect that, as with Pepys' Diary, in 200 years' time it will be in the incidental details of the Benn diaries, interspersed among the political grandees who pass through their pages - the conversation on a train with an ex- soldier who claimed he had been put in police uniform during the miners' strike; the acquisition of a wonderful new gadget, the telephone-answering machine; and the price of a cup of tea - that their real interest will lie.
Bryan Appleyard is away.