A 450-year chronicle-in-progress of the British parliamentary system gives a unique insight into every MP's life. Huw Richards reports

There were reports of "violent doings at Bridgnorth, both parties making bonfires where about one they drank Dr Sacheverell's health and the other his confusion".

So much for theories that the market towns of middle England are, and always have been, havens of peace and tranquillity.

That account of the disturbances accompanying the election campaign of 1710 in the Shropshire borough of Bridgnorth is one of myriad vignettes concealed within the five bulky volumes - totalling 5,000 pages - of the latest published section of the History of Parliament , dealing with the years 1690-1715.

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This is one reference work for which the term "monumental" refers not only to its size - 28 volumes containing 21,000 pages, 18,000 individual biographies and about 2,300 constituency articles so far - but its rate of completion. Painting the Forth Bridge is a sprint by comparison.

It can trace its antecedents to a late 1920s initiative by the maverick Labour (formerly Liberal) MP Josiah Wedgwood. An amateur historian who reckoned that "probably the Public Record Office has occupied more hours of my life than the Commons Chamber", he himself edited the first two volumes on 15th-century parliamentarians in the late 1930s, only to see academics with whom he had fallen out take revenge with savagely critical reviews.

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Restarted in 1951 with state funding - today Parliament supplies an annual grant of about ?1 million and a board of trustees chaired by Conservative MP Sir Patrick Cormack - and Sir Lewis Namier as editor, the History has been steadily chipping away at the lives of parliamentarians and their constituencies ever since. A sort of completion looms. Once the current group of projects - covering 1422-1504, 1604-29, 1640-60 and 1820-32 - are completed, the History will in its own words "provide a continuous and authoritative account of the House of Commons and electoral politics over 450 years, from 1386 to the Reform Act of 1832".

But the earliest any of these can be expected is six to eight years away, so it is wholly understandable that Paul Seaward, director of the project, admits that he hasn't thought much about the question "what after that?".

Anything so large and apparently slow-moving invites potshots. In 1964, Bernard Levin said no other government project had been "quite so entirely fatuous a waste of public money".

A. J. P. Taylor, in what Seaward labels "quite our worst review ever", argued that the MPs whose biographies form the core of the project were "persons of no importance in their own day and certainly of none in ours". He argued that "history is the record of what was significant in the past. These volumes are a record of what was insignificant."

Seaward accepts that his project's title may be a little misleading. An institutional approach, which would have focused on Parliament's procedures and actions, was rejected in favour of one that emphasised its members and how and why they got there. "If we'd adopted that approach, it would undoubtedly have been completed more rapidly. But it would also have been much less interesting and would have looked rather old-fashioned by now," he says.

The institutional approach would have been inward-looking and limited. The style adopted allows Parliament to be used as a two-way mirror - not simply understood in the context of the society of the time, but providing insights into it.

Seaward believes that Taylor accidentally identified the project's greatest strength: "We don't select in the way that the Dictionary of National Biography does - by definition anyone in the DNB is significant in the sense that Taylor meant. We set the much lower barrier of having been elected to Parliament. That comprehensiveness, together with the constituency profiles, which are our hidden treasure, gives a depth and texture to the detailed knowledge that is hard to find anywhere else."

Seaward describes the History as a prosopography, which he defines as "a collective biography, taking a cross-section of a large number of individual stories".

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He explains further: "We look at them not just as individuals, but the way in which they interact. It builds up a picture of the political and social landscape of the time, and the complete History offers the opportunity to trace how that changed over long periods."

The apparently obscure often turn out, on closer examination, to matter. "The 1820-32 study is turning up fresh information on Irish elections and politics that adds vital detail to our knowledge of the period. Work on the 1640s and 1650s is finding that members who appeared to be completely obscure played vital parts in the politics of the army in the 1650s. The 1690-1715 project turned up an unprecedented depth of information about patronage and networks. The depth of the research uncovers things other history cannot reach."

Seaward argues that the 25 researchers, divided into five-strong teams based in Bloomsbury, "are a research team to at least match any university in the country. It is hard to imagine a better training in the techniques of detailed historical research than working here." The project's approach dates back to the relaunch under Namier in the 1950s. "He was aiming to create a complete sociological cross-section. He was deeply interested in social history and believed that deep secrets could be found by piling up information about changes in classes and groups in English society," Seaward says.

The 1690-1715 period was one of financial change. "You had what was in effect a new financial system, with the creation of joint stock companies and the Bank of England. There was fierce competition for control of the East India trade. All this created a flood of money into the city and thence into politics. In tracing this and the way financiers lobbied, you can draw parallels with the 1980s and the impact of the Big Bang."

Seaward's favourite 1690-1715 passage concerns the anger of the glovers and tanners of Hereford following the imposition of a tax on leather in the 1690s, and how it was vented on local MPs Paul Foley and James Morgan. It records that "in 1697 'the leather mob - from Hereford' paid a visit to Foley at Westminster, to whom they were 'very rude', even to threaten pulling down his house. They had previously 'affronted his son and lady at Hereford' and had also insulted Morgan."

Morgan and Foley responded with efforts to repair their reputation - Morgan piloting a Commons bill to create a workhouse for Hereford, while Foley worked to secure a new charter for the city corporation in 1698.

Seaward says: "This displays the dynamic between local and national politics, between the population and the elite, all of them mixed together. It is a small illustration of what we can do."

So what next? There are long-term plans to extend the project before 1386 and after 1832. Seaward notes that the earlier period will require some definition of when Parliament started, while the far greater volume of sources post-1832 will need a change of approach. A pioneer project looking at the House of Lords from 1660 to 1832 also points to new lines of inquiry, while collaboration with the University of Sheffield's Humanities Research Centre to publish a digital version of the House of Commons Journal - the official minute book that Seaward himself helped to write in his previous job as a Commons clerk - will add a fresh institutional dimension.

But these are all long-term issues. In the shorter term, Seaward wants to see what is above all a source work for historians better known outside its core audience of professional political specialists. He is encouraged by burgeoning interest in local and family history. "There is a new public there, much of it extremely sophisticated and skilled. We frequently hear from people who will say something in one of our earlier volumes was wrong."

Josiah Wedgwood, who was historian of both family and local matters, would doubtless feel vindicated.

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