An academic has defended a university archive from criticism from a most unlikely source - Sir Winston Churchill.

New documents discovered have shown the former Prime Minister and his staff had little time for Mass Observation, a major anthropological research exercise which rose to prominence in the Thirties and is now maintained by the University of Sussex.

The project which collected the day to day thoughts of hundreds of people from different walks of life was used to gauge public opinion on a range of issues.

During the early years of the Second World War it was used by the Government to assess public morale.

More recently actors and actresses including Victoria Wood, Richard Briers and Greta Scaachi have used the archives, kept at Falmer, near Brighton, to develop characters for stage and screen.

But it evidently fell foul of the nation's most famous leader.

In recently released letters discovered at the National Archives in Kew a member of Sir Winston's inner circle describes the project as a "dirty affair", labels the correspondents as "dupes" and says the organisers were left-wingers taking bribes from companies like Unilever to give them product placement in reports.

Dorothy Sheridan, head of special collections at the University of Sussex and current director of the Mass Observation archive, said: "I knew Churchill did not like the Mass Observations but I had no idea this man had been so horrible about it.

"Anyone who has looked at the archive will know that the correspondents were certainly not dupes. They were people who wrote very honestly about themselves.

"The organisers were always very strapped for cash in the early days and they tried all sorts of things to raise money but I've never seen any mention of Unilever in the archive, and I've looked after it for decades."

The letters, written by Churchill's personal assistant Desmond Morton, described the Mass Observation as a business equivalent to the Gallop Poll.

He wrote: "It is a dirty affair. It obtains its volunteers by posing as a group with left-wing tendencies setting out to better the lot of the down-trodden poor, but actually sets its enthusiastic supporters to finding out free of charge how people like Messrs Unilever's margarine and things of that sort, for which Messrs Unilever and others pay the promoters of the scheme."

He later described Mass Observation as "an infernal nuisance and a potential danger" after the organisers asked correspondents where and when they thought the D-Day landings would take place.

After the Government withdrew backing from the project in the late Thirties it became a more commercial venture, running until the Seventies. The archive was moved to the university in 1970 by the then vice-chancellor Asa Briggs, a keen anthropologist. It has been used for academic research by thousands of students in the past 30 years and continues to be added to.

While the original correspondent system is no longer used, the university has developed hundreds of new links, allowing people to submit their diaries to the collection.

Do you agree with Sir Winston Churchill? What are the strengths and pitfalls of these sort of projects? Tell us your thoughts below.