Olinto De Pretto, an industrialist from Vicenza, published the equation E=mc² in a scientific magazine, Atte, in 1903, said Umberto Bartocci, a mathematical historian.

Einstein allegedly used De Pretto's insight in a major paper published in 1905, but De Pretto was never acclaimed, said Professor Bartocci of the University of Perugia.

De Pretto had stumbled on the equation, but not the theory of relativity, while speculating about ether in the life of the universe, said Prof Bartocci. It was republished in 1904 by Veneto's Royal Science Institute, but the equation's significance was not understood.

A Swiss Italian named Michele Besso alerted Einstein to the research and in 1905 Einstein published his own work, said Prof Bartocci. It took years for his breakthrough to be grasped. When the penny finally dropped, De Pretto's contribution was overlooked while Einstein went on to become the century's most famous scientist. De Pretto died in 1921.

"De Pretto did not discover relativity but there is no doubt that he was the first to use the equation. That is hugely significant. I also believe, though it's impossible to prove, that Einstein used De Pretto's research," said Prof Bartocci, who has written a book on the subject.

Einstein's theory held that time and motion are relative to the observer if the speed of light is constant and if all natural laws are the same. A footnote established the equivalence of mass and energy, according to which the energy (E) of a quantity of matter (m) is equal to the product of the mass and the square of the velocity of light (c). Now known as: E=mc² .

The influence of work by other physicists on Einstein's theory is also controversial. A German, David Hilbert, is thought by some to have been decisive.

Edmund Robertson, professor of mathematics at St Andrew's University, said: "An awful lot of mathematics was done by people who have never been credited - Arabs in the middle ages, for example. Einstein may have got the idea from someone else, but ideas come from all sorts of places.