A Conservative peer may have damaged his chances of being allowed back into the US after legally smoking cannabis in Colorado, a leading immigration lawyer has said. Daniel Finkelstein wrote in the Times on Monday of how he smoked marijuana for the first time at a friend’s house in the state, where buying limited quantities of the drug for recreational use has been allowed for almost a decade. But such admissions could lead to US authorities refusing future visas, because while it is now legal in several states, possession and use of the drug remains a federal crime, according to Charlotte Slocombe, a partner at the law firm Fragomen and an expert in US immigration law. Lord Finkelstein, who does not drink, smoke or even drink coffee, described how he chose to try the drug only because he knew it was legal, “and I try never to do things that are illegal”. He is unlikely to be alone if he falls foul of the legal anomaly and US authorities choose to act. Tourists have been drawn to states from New York to Oregon where the drug has been legalised for limited recreational use and is sold in licensed shops, bringing in several billion dollars in tax revenue annually. Slocombe said the US embassy “having access to social media could ask questions around use of drugs, and any admission could lead to becoming inadmissible for a visa”. She added: “You do not need to be convicted to be deemed inadmissible under US immigration.” Finkelstein, who recently became a director of Chelsea football club, which is now under new US ownership, wrote in the article that his family had “researched the law quite carefully. Where could we buy it, where could we smoke it, who could smoke it.” He and his eldest son then bought a strain of cannabis called Jelly Pie from a shop called Half-Baked in Boulder and Finkelstein tried it a few days later. “The effect wasn’t great,” he wrote. “It didn’t change my life. After my second drag I told the others that I had now decided I was against capitalism and nuclear weapons, but in truth I was just the same as before, except very gently mellow.” When a legal blog highlighted on Twitter that he may have fallen foul of the anomaly that possession and use of cannabis in states such as Colorado and California is legal while remaining banned federally and that he could be banned from the country, Finkelstein replied: “They checked my passport before selling me the drug so I don’t think so.” But Slocombe said the visa waiver, known as an Esta and used by many travellers to the US, asks: “Have you ever violated any law related to possessing, using, or distributing illegal drugs?” Anyone answering yes would become ineligible and would need a full tourist visa, and the application for that asks a similar question. She said: “There are more instances of issues at the border with customs and border protection than at US embassies, but yes there is a real issue, particularly along the Canadian/US border because it is now legal in Canada.” Finkelstein and Chelsea FC have been contacted for comment.