A suspected plot by muslim fanatics to destroy the heart of London was smashed yesterday in a high-seas raid on a cargo ship.More than 20 tonnes of plastic explosives-enough to blow up Parliament-are feared hidden aboard the MV Nisha.The search of the 26,000-tonne cargo of raw sugar could take days.The ship was siezed 30 miles off the English coast after a tip-off from MI6 agents in the Middle East.A Special Branch source in London said: "This is not a speculative operation.""We have information that that the ship was loaded in Yemen with a large consignment of explosives, which were to ...