The court heard how they had entered the Marconi shipyard at Barrow-in-Furness, Cumbria, in November 1999, armed with hammers and other tools.

I had been prepared for a prison sentence and had actually packed a bag when I came here this morning

Sylvia Boyes

They intended to damage the nuclear-powered submarine while it was being prepared to undergo sea trials, although it had not yet been fitted with its Trident missile warheads.

The pair admitted their actions, but claimed they were justified because nuclear weapons were "immoral and illegal".

Mrs Boyes' barrister, Terry Munyard, told the jury: "History is littered with people who broke the rules because they were acting in the interests of justice and in doing so paved the way for a better and a more humane society."

The jury at Manchester Crown Court accepted the defendants' claim that as they were upholding international law they themselves were not committing an offence.

Action will continue

Outside the court, Mrs Boyes, who burst into tears as she was welcomed by supporters, said: "I am very happy."

"It was totally unexpected. I had been prepared for a prison sentence and had actually packed a bag when I came here this morning.

"I will continue with this until we get rid of Trident."

On leaving the court, River, an Open University lecturer who had conducted his own defence during the week-long trial, said: "I hope now the government will listen to the conscience of yet another jury who have shown them the public are not willing any longer to accept weapons of mass destruction held and employed in their name."