I have not been able to follow events as closely as I would like on the run from the British authorities but it has been brought to my attention that there is some dispute over the disclosure that Peter Mandelson's phone was bugged in the 1970s.

I reviewed Mandelson's PF (personal file) in the run up to the general election in 1992. There were two main volumes which contained incoming relevant intelligence from the telephone tap and other sources. I think there were also supplements to the main volumes which contained the abundant tittle tattle that any telephone tap produces. Officers would not usually call these up during a review so I did not. And, on the basis of reading the main volumes, I had already decided that Mandelson did not pose any realistic threat to national security so there was little point in calling up the supplements.

I clearly remember that Mandelson was the target of an intecept because there was a warrant on the minute sheet of the file. (This was a curious convention of MI5: each sheet filed was logged on the minute sheet kept inside the front cover. Any warrants were also written on this sheet). In the days before the Interception of Communications Act, MI5 gave very brief reasons to government for their activities, if at all, and Mandelson's case followed this pattern.

MI5 had a number of reasons for investigating Mandelson. In 1977, he went to Cuba as part of the World Democratic Youth Festival, organised by the Eastern Bloc and dubbed by MI5 as a "Communist front organisation." The Foreign Office was aware that Mandelson was already displaying his considerable political skills in organising it at the British end. Someone had, however, tipped them off that Mandelson was some kind of covert communist who could not be trusted.

The Soviets deeply distrusted any officials of the Communist Party of Great Britain because they knew that the Party was heavily pentrated by MI5 and Special Branch agents. However, the Soviets needed to recruit their own agents and they wanted people with ideological commitement to the communist cause so they targeted those in the CPGB who had not become prominent. If the recruitment was successful, the new agent was told to renounce publically his communist allegiance, as had happen with Kim Philby et al.

Mandelson had joined the Party proper in 1973 but soon after began to pursue more mainstream politics in the student and trade unions. He then only mixed with communists as part of his day to day legitimate political activities. To MI5 and the Foreign Office, he fitted the profile of a Soviet sleeper.

We may have greater sympathy for MI5, if we understand that at the same time the organisation had good intelligence to indicate that a number of leading left wing politicians, trade unionists and journalists were in the pay of the Soviets. Gordievsky, the head of station in the UK who later defected, confirmed that one prominent left winger at least was a KGB agent who had passed state secrets to the Soviets.

In this atmosphere, MI5 decided to tap Peter Mandelson's phone. I cannot remember much about the product from the intercept operation other than Mandelson was a devoted politico who had little time for women or socialising. The tap showed that Mandelson appeared to be a moderate left winger who put considerable effort into trying to bring the extreme left around to his point of view. Ironically, this counted against him as it could, in the minds of the paranoid, be interpreted as cover for his covert communist activities and sympathies.

Crucially though, there was no indication from the tap or the agents who occasionally reported on Mandelson that he did any of the things inherent in spying. There was no indication that he met a Soviet handler or any suggestion that he was trying to communicate with the Soviets. In the course of his work, Mandelson did meet Soviet agents publically but there was nothing to show that Mandelson knew they were working for the Soviets.

So why did the intercept go on so long? It appears that MI5 was victim to one of its long running problems. There is such a lack of leadership that no one dares to make a decision. The investigation appears to have been allowed to drift with the tap being renewed as necessary. But no one was prepared to summarise the findings of the investigation or to take more positive action one way or the other. Sometimes in these cases, the target was interviewed by MI5 but Mandelson was not. In the end the intercept was quietly cancelled.

Mandelson's final categorisation was '1977; member; communist'. That is why his file was still open in 1992 when I came to review it. After five years without any proof that he was a communist, it would go amber. Then, after a further 10 years it would go red, meaning it was effectively closed (even during this period, it could still be called up and read and some types of papers could be filed on it). Mandelson's was due to go red later in 1992.

So to sum up, there was no indication that Mr Mandelson's activities were anything other than legitimate political protest. The intelligence case against Mandelson in the first place was extremely thin and the decision to tap his phone was a typically MI5 knee jerk reaction, one which still prevails today. I believe it was highly unlikely the telephone intercept would pick up anything of great value as, if Mandelson had been a Soviet sleeper, he would have been taught telephone and operational security. Contrary to popular belief, technical sources do not provide the best intelligence. Human agents do. MI5 would have been better off recruiting agents to report on Mandelson.

I still believe it was neither morally or indeed financially justifiable for MI5 to invade the privacy of political activists, if their activities did not directly threaten democracy or the state.

So who is saying that MI5 did not tap Mandelson's phone? Is it Mr Lander or Mr Mandelson? If Mr Lander thinks what I said is not true, why didn't he brief ministers four weeks ago? Why isn't he lobbying all concerned with his version of the truth so we can all see what it is and examine it in detail? Perhaps as a government official paid over £80,000 a year of taxpayers' money, it is time Mr Lander demonstrated value for money. Let's have a detailed on the record response to the British public in person stating MI5's views on my specific disclosures. Or is he afraid of having to answer awkward questions from enquiring journalists?

Mr Lander is a shrewd tactician, especially in the ways of the Men in Grey in Whitehall and their relationship with government. MI5 cares little about media and public opinion when it comes to its image and its work and has managed to convince previous ministers that this should be the case. Both Labour and Conservative ministers have swallowed this line on public opinion for fear of being accused of being soft on national security and crime.

Mr Lander knows that he only has to have the confidence of government ministers - rather than of parliament and the people who elected them. He is also aware that MI5's position would be considerably weakened if Mr Mandelson started to whisper in the ear of the prime minister, a man who listens to Mr Mandelson's advice and is ultimately responsible for the conduct of MI5. Mr Lander for this reason appears to deny the revelations concerning Mr Mandelson.

There is of course one way to settle this dispute. Show the file in its entirety to Mr Straw, Mr Mandelson and the entire parliamentary security and intelligence committee. And why not parliament? After all, nearly all the information will be over 17 years old and it is difficult to see how its release could compromise national security now, especially as by MI5's own admission there is no threat from the Communist Party. But that may be too much for an organisation which has never willingly released a document to the public since its inception in 1909.

I chose a career in MI5 because I believed in serving my country and protecting the freedom of the British people from those who genuinely aimed to undermine the democratic process. It is then ironic that I have been gagged by those who are supposed to be protecting our freedoms. No one seems interested in ressurrecting Britian's tradition as the most liberal country in western Europe until the 1970s or enshrining in a constitution the rights that citizens have in most other democracies .

When Cathy Massiter made her allegations against MI5 in the 1980s, she revealled details of ongoing operations and even the name of an agent. The authorities took no action against her. In my article, I was careful not to reveal the identities of MI5 staff; compromise the security of agents; nor hamper the legitimate work of MI5. So why take action against me and arrest my friends? Is MI5 becoming more draconian at the very time it is supposed to be increasingly open and accountable?