The court heard the operation could have had a huge impact

The group produced and distributed forged British and European bank notes between August 2005 and April 2007 from a Glasgow print shop.

The High Court in Edinburgh heard the operation was so sophisticated it could have threatened the UK economy.

The six men are due to be sentenced together next month following background reports.

John McGregor, 49, could receive a maximum sentence of 10 years after admitting making fake Bank of Scotland �20 notes.

Thomas McAnea, 57, denied the same charge and his plea was accepted by the Crown, but he admitted delivering, selling or disposing of fake notes.

Police had begun undercover surveillance on the gang after suspicion arose in England that a multi-million pound operation was being run from Glasgow.

Admitted roles

Two other men, Joseph McKnight, 56, and Robert Fulton, 62, both from Glasgow, were convicted of helping to distribute counterfeit money.

McKnight was caught with almost �7,000 and 7,500 euros of forged currency and Fulton was found with more than �6,000 and 3,000 euros of forged notes.

Two other men, Rodney Cadogan, 39, from London, and Steven Todd, 23, from Glasgow, also admitted roles in the money-making scheme.

Cadogan was caught with more than 100,000 euros and Todd admitted delivering, selling or disposing of forged notes.

McAnea and McGregor had been convicted of producing fake �5 and �20 notes and jailed in 1998 but were freed on appeal in 2000 because of a typing error.

Search warrants used by Strathclyde Police when officers conducted raids in 1996 were invalid because the date of the Forgery and Counterfeiting Act was typed as 1989 instead of 1981.