Security services around Europe are on alert to a potential new weapon of Russia’s war – arson and sabotage – after a spate of mystery fires and attacks on infrastructure in the Baltics, Germany and the UK. When a fire broke out in Ikea in Vilnius in Lithuania this month, few passed any remarks until the Polish prime minister, Donald Tusk, suggested it could have been the work of a foreign saboteur. Investigators have already alleged potential Russian involvement in an arson attack in east London, an inferno that destroyed the largest shopping mall in Poland, a sabotage attempt in...