By Tommy Wilkes and Simon Jessop LONDON (Reuters) – When the East Sussex local authority pension fund in southern England wanted to cut its exposure to fossil fuels, it needed to be sure there were no oil and gas stocks in the benchmarks its passive funds tracked. So the scheme recently swapped 200 million pounds ($271 million) out of a passive fund that tracked a traditional equity index into one that excludes oil, gas and coal companies. That has helped it reduce its exposure to fossil fuels to below 2% of assets today — from 6% in 2016 — said Gerard Fox, chairman of the pension fund commi…