A Dutch judge upheld the government's plan on Friday to introduce a "weed pass" preventing foreigners from buying cannabis in coffee shops in the Netherlands.
Amsterdam, whose scores of coffee shops are a major tourism drawcard, opposes the plan, and mayor Eberhard van der Laan says he wants to hammer out a compromise.
A lawyer for coffee shop owners said he would file an urgent appeal against the ruling by a judge at The Hague District Court that clears the way for the introduction of the pass in southern provinces on May 1.
The pass will roll out in the rest of the country - including Amsterdam - next year. It will turn coffee shops into private clubs with membership open only to Dutch residents and limited to 2,000 per shop.
The changes are the most significant rollback in years to the traditional Dutch tolerance of cannabis use.
Foreign Minister Alistair Burt's admission that the Cameron government has "supported" a survey of attitudes to US drone strikes in Pakistan's tribal areas amounts to a tacit admission of British involvement.