Who got there first?

Successful tests on a German device manufactured in 1863 were covered up to maintain the Scot's reputation, the previously unseen files have revealed.

They show the "Telephon", developed by German research scientist Philipp Reis, could transmit and receive speech.

It is alleged UK businessman Sir Frank Gill was behind the cover-up.

The evidence is contained in files from the archives of the Science Museum in London.

The documents were rediscovered in October by the museum's curator of communications, John Liffen.

Contract bid

Gill was chairman of Standard Telephones and Cables (STC), the company that conducted the tests on Reis's' device.

The company was at the time bidding for a contract from the American Telephone and Telegraph Company, which evolved from the Bell Company.

Gill thought that if word got out of the test results, it would scupper STC's chances of winning the contract.

Some researchers have argued for many years that Reis beat Bell to the invention of the telephone. The archived documents seem to support their claims.

A memo, dated 18 March 1947, from Gerald Garratt, a predecessor of Mr Liffen's, show STC's reports on Reis's device were given to him under the strict condition that they would never be publicly referred to or published without permission.

STC then became anxious to retrieve the documents. In a subsequent letter, Garratt wrote: "I am left with the thought that there is something so secret about [the documents] as to be a matter of first class historic interest.

"You must know as well as I the old controversy: 'Did Bell invent the telephone?' and I have here an unpublished manuscript of over 400 pages which proves pretty conclusively that he didn't.

"Does your anxiety to retrieve these reports rather suggest that you agree?"

In 1955, LC Pocock, a research scientist in STC's acoustics laboratory, wrote a letter to Garratt explaining: "[Frank Gill's] decision was that he didn't want the STC name mentioned in any further controversy that may arise as a result of the Reis device."

The "Telephon" could transmit speech very faintly. It could receive good quality speech but only at a low efficiency.

"If by telephone, you mean a device that could communicate over any sort of distance, then [Reis] did invent the telephone," said Mr Liffen.

Scottish-born scientist Alexander Graham Bell is often credited with making the first transmission of speech from one point to another by electrical means in 1876.

But, as with so many of these "world firsts", there are competing claims. Researchers Antonio Meucci and Elisha Gray were also known to be working on speech transmission devices at the same time as Bell and Reis.