David James described how he used 'banking contacts' to end a year-long search for the gun all over Europe by MI6 and other intelligence agencies. He claimed there were 'whoops of joy' from MI6 when told.
He told how he arranged for up to 1,000 documents about the supergun to be taken from a factory making a prototype of the weapon and secretly photographed overnight for MI6 before being returned unnoticed.
Mr James, chairman of Eagle Trust, the former parent company of Walter Somers, a Halesowen-based foundry which made parts for a prototype gun, said he first saw tubes which formed part of the gun while routinely visiting Walter Somers. In spite of the fact it was 'full of pipes as far as the eye could see' he noticed three unusual pipes. He said one stood out because it had a 'thumping great muzzle like a strip-cartoon siege gun'.
He said Peter Mitchell, Walter Somers's managing director, had said it was for an Iraqi petrochemical plant and reassured him the authorities knew all about it and had cleared it. In spite of this, further discreet inquiries 'gave him grounds for far greater concern'. It prompted Mr James to 'make a phone call to MI6. I rang them up and told them what we had got in the factory and asked if it was any use to them.'
Mr James said his contact - described as Mr Z - asked for a meeting at which he asked for more details. Mr James said he showed Z and an MI6 artillery expert rough sketches and other details. Both men, he claimed, were disappointed.
Mr Z informed him European intelligence services had been hunting for the components of a bigger 'monster gun' described as Project Babylon - believed to be being manufactured somewhere in Europe - after a tip-off from the Israeli intelligence service, Mossad. They asked him to help find out if any bigger gun parts were being made.
Using 'banking contacts' he found that Sheffield Forgemasters was building a much bigger gun. Customs later seized the Sheffield Forgemaster 'tubes' on the dockside at Teesport before they were sent to Iraq.
MI6 told Mr James it was a 'major intelligence coup'.
Mr James said he withheld evidence of MI6 links from a House of Commons select committee investigation for several reasons, including 'personal safety'. He denied he or any Walter Somers employees were coached by MI6 about what to say. He had since decided it was in the 'national interest' that the full facts be told.
The hearing continues in public next week.