TWO Black Watch soldiers were last night sent back to Britain after being discharged from the British Army for drug offences. Private Robert Petrie Clark and Private Bruce Alexander McGilvray were told to pack their bags early yesterday, 11 days after each was fined $2,000 in Eastern Court for possession of the drug Ecstasy. The two teenagers could not face any military discipline because of laws prohibiting them being tried twice for the same offence. They had been performing their usual duties until the discharge notices were issued. Garrison spokesman Roger Goodwin confirmed that Clark, 19, and McGilvray, 18, were flown back to London. ''The army will not tolerate drug abuse in any shape or form wherever it is found,'' he said. ''Clearly we could not take action while the civilian case was pending. Now that has been completed, the commanding officer Lieutenant-Colonel Sir Andrew Ogilvy-Wedderburn Bt has exercised his power to administratively discharge these two. ''While Ecstasy may not be a proscribed drug in Hong Kong, it is a proscribed drug in the army. ''It is quite clear from the case that they were in possession of Ecstasy and the commanding officer has taken the appropriate action.'' The two men were prosecuted under the Poisons Ordinance though the Narcotics Division is now preparing amendments which would add Ecstasy to the list of dangerous drugs. Army regulations state that anyone found guilty in a civilian court of a drug-related offence can be discharged. Clark and McGilvray, who are both single and had been based at Stanley Fort, will not receive any favourable references from the army and they would have lost any pension rights had they been in the army long enough to qualify. Mr Goodwin said the Armed Services remained highly vigilant against any drug abuse, but denied that routine searches of personal belongings were being established except where there were grounds for suspicion. ''We have never tried to suggest that drugs do not exist in the British Army,'' he said. ''The army is a reflection of the society from which its members come, but the services will not tolerate drug abuse in any shape or form. ''A very close eye is kept on these things, especially in Hong Kong simply because of the availability and temptations,'' he added.