People realised in ancient Babylon that soap, or something like it, could keep you clean, reduce body odour and perhaps make you a bit nicer to know. So the fortunes of soap have been linked to fluctuations in the rise of personal cleanliness - big in Roman times, not so big, say, in 14th-century Britain.

But it wasn't until the general acceptance of "germ theory" in the early years of the last century that the link was made between soap and the prevention of disease. That stern phrase "now wash your hands" quite rightly conjures up visions of fearsome Edwardian matrons with blocks of pink carbolic.

"The use of soap for controlling disease is really quite recent," says Suzanne Taylor, research assistant in the history group at the London School of Hygiene and Tropical Medicine. "Germ theory began in the 1870s, but it wasn't till the early 1900s that people were giving lectures and handing out postcards saying hand washing could stop disease."

Her research, funded by Unilever and linked with a project to prevent disease through handwashing in Ghana, is a slightly offbeat example of the work of the history group, which profits from a unique relationship with the scientific staff of the school to study British health and the making of health policy in the 20th century.

Other examples are a conference last December on the 1952 Great Smog of London and the reforms it provoked, research on the growing role of the media in health matters, a historical study of policy on diet and heart disease and others on anti-smoking campaigns and the growth of medical technology. Most of this was part of a project programme called "science speaks to policy", funded by the Wellcome Foundation Trust .

The impact and reputation of this work has been so strong that the group is about to expand, change its name to the Centre for History in Public Health, take on more staff and create a management committee that will include more members of other departments of the school. There'll also be a bigger, improved website. It's a coming of age for the only organisation of its kind in the UK.

"The changes will improve our formal links to scientists in the school, make us more visible and give us the opportunity to do things in a more consistent and systematic way," says Virginia Berridge, professor of history and head of the history group, who first came to the school in the 1980s to research and write a book about the development of UK policy on Aids.

"It's quite an unusual way for historians to work - we're more used to working as lone individuals, without relating very much to other people. Historians tend to go off to libraries and settle down with the archives. The scientific model is teamwork, and we're moving closer to that, although we use archives and oral history."

Berridge's main aims in the new set-up are to consolidate the practice of contemporary history of public health matters, and to persuade policy-makers to take that history into account. This will be made easier by the recent appointment of an archivist, Victoria Killick, who is bringing together and making accessible a range of health-related documents and artefacts deposited over the years in nooks and crannies of the school's 1929 Art Deco building in Keppel Street.

"A lot of the archive material is to do with tropical diseases, such as the notebook of Ronald Ross when he was discovering the link between malaria and mosquitos," says Killick. "There's a lovely diary of a couple researching sleeping sickness in Uganda in the 1930s, and a good collection of photographs of people with diseases like elephantiasis. But there's plenty of more modern material, too."

The new focus on the contemporary history of public health by Berridge and her colleagues will include studies of health publicity material in recent decades, public health policy in relation to cancer and the differing practice on drug addiction treatment in the private medical sector and the NHS.

Berridge feels there's a tendency in Britain to ignore the lessons of recent history in the formulation of health policy. She says the current approach to drug addiction, for example, is more likely to refer to what's being done in other countries than to look at what happened to drug treatment initiatives here in the 1960s.

"However, I'm very pleased that I'm being asked to speak to the Cabinet Office about the history of alcohol as a legal drug as part of their current discussions on the new government alcohol strategy," she says. "History can indicate that particular ideas or practices have been on the agenda before. In the late 1970s and early 1980s the central policy review staff also formulated an alcohol strategy and it will be very interesting to see if the lessons of the history of that strategy have really been learnt.

"Similarly, the debate about foundation hospitals has made very little reference to history, and yet what's being proposed is very much related to the system of voluntary hospitals which operated before the establishment of the NHS. So often, public debate happens without that important historical dimension."

She adds: "I think it could be brought into the debate more and I think many other historians agree. We used to take the attitude that you did history for history's sake. But the fact that history is now so popular, for example with people doing their family histories and with so much history on the BBC, has meant historians becoming more involved and more aware of the public repercussions of their work - and the policy aspect, too."

But Berridge also cautions against historians being drawn into politics. In the US, she says, historians have taken such a high profile in policy that when governments change, historians are changed as well: "We have to be wary of that kind of relationship, where you become in effect a policy poodle."

She also warns that historians must be aware that they can't always keep control of their work, which might be used or interpreted by politicians or pressure groups in ways they might not like. "Some historians think they have only to say what happened in history and policy will be changed, but it's not like that," she says.

"An example is drugs policy, where I wrote about the legal use of opium by people in the 19th century. I actually argued that the transfer of past experience to the present is very difficult, but there has been a tendency to use the research as an argument for the legalisation of drugs. It was never presented as such, but one doesn't have any control.

"People don't always understand the issue of historical distance - that researching or analysing a subject doesn't mean you're morally committed to it. Another example is the links that public health had with the tobacco industry until the late 1970s because of the joint agenda of harm reduction. We don't refer to that in order to point the finger and say that policy was the tool of the tobacco industry, or conversely to say we should go back to that pattern. In the polarisations of the policy world, that's a difficult stance to take."

· The history group's web pages can be found on www.lshtm.ac.uk