By Susanna Twidale LONDON (Reuters) -Britain’s National Grid, which operates the Isle of Grain liquefied natural gas (LNG) terminal said it is seeking to understand if a block on Russia-related vessels, announced by the British government on Monday, includes LNG shipments. Britain on Monday ordered its ports to block any vessels that are Russian-flagged or believed to be registered, owned or controlled by any person connected with Russia as it ratcheted up the pressure on Moscow. “We are supportive of government action to order UK ports to block all Russian-linked ships, and are seeking to und…