By Kirstin Ridley and Pratima Desai LONDON (Reuters) – U.S. hedge fund Elliott Associates and Jane Street Global Trading are invoking the Human Rights Act as they seek to sue the London Metal Exchange (LME) for a combined $472 million over its decision to cancel nickel trades in March. The nickel trading debacle is the biggest crisis to hit the world’s oldest metals forum in decades. Elliott and Jane Street, which are demanding damages of $456.4 million and $15.34 million respectively, are seeking a judicial review after the nickel price topped a record of $100,000 per tonne on March 8, prompt…