By Ron Bousso LONDON (Reuters) -A British regulator is expected to approve in the coming days a revised plan by Shell to develop a North Sea gas field, which had been initially rejected on environmental grounds, three sources told Reuters. Shell released in March its updated environmental development plans for the Jackdaw field to the Britain’s Offshore Petroleum Regulator for Environment and Decommissioning (OPRED). Under the new plan, Shell aims to start production from the field, which will supply 6.5% of Britain’s gas output, by the second half of 2025. OPRED had in October, on environment…