'Belgrano' ordered to attack British ships on day before sinking, secret report reveals

New official history may finally settle controversy over destruction of Argentine warship with loss of 323 lives

The Argentine cruiserGeneral Belgrano was ordered to attack the British fleet the day before she was sunk at the start of the Falklands War, according to secret intelligence reports that are soon to be released.

The sinking of the Belgrano is one of the greatest controversies in modern British military history. The cruiser was outside a 200-mile exclusion zone and sailing away from the British fleet when it was torpedoed, with the loss of 323 lives, by the submarine HMS Conqueror on 2 May, 1982.

A new official history of the war will claim that, according to previously undisclosed intelligence material, the Belgrano was under orders to attack the British navy. Opponents of the war accused Margaret Thatcher, the then Prime Minister, of ordering the sinking of the Belgrano although it did not pose a threat at the time. Tam Dalyell, Labour MP for Linlithgow, led a ferocious attack on Mrs Thatcher, accusing her of misleading the House of Commons.

Professor Sir Lawrence Freedman, the author of the official history to be published next year, told The Independent on Sunday: "The intercept confirms that the Belgrano was under orders to attack on May 1. It does nothing to confirm the contentions of Mr Dalyell and broadly supports what was said by the government at the time."

Professor Freedman's book exonerates Lady Thatcher, who consistently argued that the warship posed a threat to the Task Force. Signals intelligence intercepted by GCHQ, the security services' eavesdropping centre at Cheltenham, the day before Conqueror fired its torpedoes at the Belgrano, showed that the warship was under orders to attack. It is unusual for such raw intelligence material to be published.

The official history will also contain an account of a near-mutiny by members of the special forces. The commander of the SAS "B" unit refused an order to carry out a search-and-destroy operation of missile bases on the Argentinian mainland because, he claimed, it amounted to a "suicide mission".

Tony Blair commissioned Professor Freedman, director of war studies at King's College London, to write the official account in July 1997. The publication has been repeatedly delayed by rows over what can be included. Intelligence chiefs have now relented on the question of whether the key intercept could be made public. Officials at GCHQ were said to be worried that doing so could set a precedent and give away operational secrets.

Officials and ministers have always insisted that, far from heading home, the Belgrano was sailing west to a point outside the exclusion zone from which it was to attack.

Earlier this year the ship's captain, Hector Bonzo, admitted that the Belgrano's decision to sail away from the Task Force on the morning of 2 May was only a temporary manoeuvre.

"Our mission ... wasn't just to cruise around on patrol but to attack,'' Captain Bonzo said in a television interview in May. "When they gave us the authorisation to use our weapons, if necessary, we had to be prepared to attack. Our people were completely trained. I would say we were anxious to pull the trigger.''

In 1994 the Argentine government dropped its claim that the sinking of the Belgrano was a war crime, its defence ministry conceding that it was "a legal act of war''.

Last night Mr Dalyell insisted that questions still remained unanswered about the sinking of the Belgrano. "I find it extremely odd that this has popped up now after all these years when they could have easily produced it at the end of the war," he said. "I will read the full account with interest."

Sir John Nott, the Defence Secretary at the time, hinted at the existence of the intercept in his recently published memoirs. Senior ministers were "aware" that the ship was being organised in a "pincer movement'' at the time of the attack. Last night Sir John said he stood by the decision to sink the ship. "I remain astonished to this day that anyone should consider the momentary compass bearing of the Belgrano's passage to be of any consequence whatever," he said. "Any ship can turn about in an instant."

Despite the fact that the intercept supports the official position, a Foreign Office official said that Professor Freedman had faced deep opposition within Whitehall to the decision to publish it: "It has been a long haul, but we are confident that it will be published next year. You have got to remember that the Falklands was only 20 years ago, so a lot of the operational stuff is still sensitive.''