A Scot faces up to seven years in an Estonian jail after admitting smuggling 20kg of opium, worth an estimated (pounds) 714,000, through Tallinn, the capital of the Baltic republic.

William Hain, 42, was arrested in November last year while boarding a ferry bound for Finland after police found 20

packages of opium hidden in his car's petrol tank.

Ketlin Jaani of the Estonian prosecutor's office said Hain pleaded guilty to one charge of smuggling narcotics and could face up to seven years in jail when sentenced later this week.

He said the opium could be used to produce about 6.5kg of heroin worth (pounds) 1m on the streets. The seizure was the largest in the former Soviet republic's history.

An Estonian man, Sergei Petrenko, 41, was arrested with Hain and pleaded not guilty to one charge of trafficking in

narcotics.

The Estonian authorities believe the opium was en route to Scotland from Afghanistan and say Hain was arrested following a month-long sting operation involving Scottish and Estonian law enforcement authorities.

Law enforcement agencies throughout eastern Europe and the former Soviet Union have stepped up efforts in recent years to combat the flow of heroin from central Asia, particularly Afghanistan, to western Europe and north America.

Estonia is also seeking the extradition of two Scots who it says organised the smuggling operation.

Leslie Brown, 44, a company director from Bearsden, and Robert Wright, 34, from

Bathgate, have fought a long legal battle against extradition from Scotland.

In March they appeared in court in Edinburgh where a

sheriff ruled they should be sent to Estonia to face the charges.

Jim Wallace, the justice minister, agreed with the sheriff, but the two men are believed to be

seeking a judicial review of the decision.

Hain, 42, a former soldier who recently ran a pub in West Lothian, is said to have been paid to transport the drug and was provided with the money to buy a car.

Estonian prosecutors claim the three Scots and Petrenko were seen meeting several times.

Hain is alleged to have driven the car to Estonia and arrived in Tallinn, where he met Mr Petrenko who provided garage space. It is claimed that Mr Wright and Mr Brown flew in to meet the others before flying back to Scotland.

Mr Wright is well known in Scotland as a millionaire racing car enthusiast. He made his

fortune in the security business and has his own Formula One racing car.

He and Mr Brown were arrested by the Scottish Drugs Enforcement Agency in Glasgow.

Police fear that heroin from Asia is passing through Russia to the Baltic states and then being sent to Scotland as an alternative to the heavily-policed southern UK entry ports in England.

A Foreign Office spokesman said last night: ''We have heard from the courts in Estonia that Mr Hain today pleaded guilty to one drug smuggling charge.

''His trial continues and we expect it to resume tomorrow.''