Police break arms and forgery network: Several people are held after 20-month undercover operation. Terry Kirby reports

SEVERAL people were being questioned last night after detectives said they had smashed an extensive criminal network supplying semi-automatic firearms, ammunition, knives, explosives, huge amounts of counterfeit currencies and forged documents to the rest of the underworld.

Commander Roy Penrose, head of the South East Regional Crime Squad, who led the 20-month -police undercover infiltration of the London-based network, codenamed Operation Mensa, said yesterday: 'Their motto was 'If you want it, we can get it'.'

Operation Mensa culminated early yesterday in a series of raids by 150 regional crime squad detectives in London, the Home Counties, Dorset, Devon and the Thames Valley.

Last night, 27 people were being questioned at several different police stations and police said the operation was still continuing.

Mr Penrose said that although the criminal network was organised and involved people who earned 'vast amounts' of money through crime, it was a loosely structured affair and not an hierarchical body like the Mafia. 'These people came together on an entrepreneurial basis to fund their lifestyles,' he said.

At a farm in the Dorset village of Toller Porcorum, police uncovered what may have been the network's arsenal, a store of more than 40 automatic and semi-automatic weapons, large amounts of ammunition, flick-knives and daggers. The firearms included two AK47 Kalashnikov assault rifles and a flint- lock rifle. A 40-year-old man was arrested.

Acting Det Supt Tony Rogers, who led the Dorset operation said the weapons were still being examined and categorised, but that he had 'no doubt whatever' that they were destined for the hands of criminals.

In London other raids uncovered a Second World War German-made Schmeisser sub-machine gun, shotguns and ammunition, 2kg (4.4lbs) of PE4 military-style plastic explosive and detonators.

Mr Penrose said the PE4 was being offered to the underworld as samples for a sale of two tons at a price of pounds 3,000, although it was believed that the criminals did not actually have the explosive and were involved in a confidence trick. The explosives and detonators are not believed to have any terrorist links - the IRA normally favours Semtex or home- made explosives.

Detectives believe the counterfeiting and forgery operation was one of the biggest of its kind ever discovered. More than pounds 1m in forged pounds 50 notes - which had been sold for pounds 30 each on the black market - and dollars 200,000 ( pounds 100,000) in dollars 100 bills were recovered earlier and a further pounds 500,000 in counterfeit sterling and dollars 50,000, printing plates and other plates for Danish Kroner were found yesterday.

Among the large amounts of forged documents seized were MOT certificates, birth certificates, disabled parking badges, building society cheques and travellers cheques. The forged cash and other documents are said to be of extremely high quality and police believe many notes are in circulation.

Police also recovered stolen vehicles, including a JCB excavator. Mr Penrose said: 'You can never be sure you have cut out cancer, but we are happy that we have made a severe dent in the counterfeiting fraternity.'