Customs officers at a London airport yesterday found 50,000 pounds worth of drugs which were being smuggled (走私) into Britain in boxes marked "Urgent Medical Supplies". The authorities might have suspected for some time     1    drugs would be brought into the country in this way. The operation is believed to be the work of a     2    international group. Four men were arrested at     3    airport and held for questioning,     4    it is unlikely that they are the organizers. In     5    they declared that they were     6    of what the boxes contained and had acted in good faith in bringing     7    into Britain. This is the third time     8    six months that attempts have been made to smuggle     9    goods through Customs by declaring them to     10    medical supplies. They are frequently     11    in special containers and a note is given that they may be damaged if they are not handled with care. "    12    are determined to put a     13    to this practice," said one of the Customs officers today. "    14    is no way these people are going to get away     15    this any longer. We have the full co-operation of the international police to track down the main source of supply."