By Sruthi Shankar (Reuters) -UK’s FTSE 100 fell on Tuesday, tracking a sour global mood with energy stocks leading declines and shares of British utilities slumped after a media report fuelled speculation of a windfall tax. The benchmark FTSE 100 fell 0.4% with oil majors Shell and BP among top drags, while the midcap FTSE 250 dipped 1.5%. UK power generating companies Drax, Centrica and SSE plunged between 13.8% and 7.9% after the Financial Times reported that the British government planning a possible windfall tax on more than 10 billion pounds ($12.48 billion) of excess profits by electrici…