The former foreign secretary, Lord Howe, was among those who protested to the Government about the claims being made in the television documentary and book, The Last Governor, by Jonathan Dimbleby.
Mr Patten's friends claim the "Hong Kong mafia at the Foreign Office" is trying to get its revenge against Mr Patten, who was reviled for upsetting China with his drive towards democracy before the final handover. They are furious with Mr Patten for claiming that Britain entered into a gentlemen's agreement with China to renege on its promises and to manipulate a test of public opinion in 1987 to suggest that Hong Kong did not want democracy.
Lord Howe attacked the book as "lamentable" and rejected its "surreal and unjust accusations of betrayal and treachery and foul play by senior government ministers and civil servants".
It is understood that protests were also made to the Government by Lord Wilson of Tillyorn, Mr Patten's predecessor, and Sir Percy Cradock, who was Margaret Thatcher's chief adviser on China.
Peter Mandelson, minister without portfolio, confirming that an investigation was under way, said he did not know if Mr Patten would be prosecuted under the Official Secrets Act. "All I know is that the issue - the matter, rather than the individual - is under investigation by the authorities," he said. "That will be done in a proper, objective and authoritative way.
"They have no alternative but to investigate it when allegations are made that secret intelligence material has been passed to individuals outside," Mr Mandelson told BBC Radio 4's The World This Weekend.
The Foreign Office was officially avoiding comment but senior Whitehall sources last night confirmed that MI6 was carrying out the investigation into whether the Official Secrets Act had been breached.
"We are not pointing the finger at anyone, but it is true to say that an inquiry is being carried out," said the source. "Breaking the Official Secrets Act is one of the most serious offences. There is genuine concern about the intelligence reports being leaked along with highly sensitive reports. That could have been very serious.
"The stage we are at at the moment is to see whether there has been a breach."
Foreign Office officials are waiting to see whether the evidence is strong enough to warrant a prosecution against Mr Patten for allegedly leaking classified documents. Sir John Coles, head of the diplomatic service, is angry that details of papers he allowed Mr Patten to see appear to have been divulged.
None of the papers were quoted directly but officials believe there items which appeared in the book and could only have come from the papers. Mr Patten saw the government papers from the mid-1980s earlier this year, before he stepped down from office, on the understanding that they would not be revealed and would be destroyed after he read them.Reuse content