British tourists coming to France for the ski season have been warned by their own government to be careful when drinking at high altitudes. The UK Foreign Office (FCO) campaign comes after more than 30 Britons died in Alpine ski resorts last year. Many died because they underestimated the risk of drinking at a high altitude, according to British diplomats.   A study published by the FCO estimated a third of skiers and snowboarders under 25 had experienced problems abroad linked to a mix of altitude, adrenaline and alcohol.