LONDON, July 9 (Reuters) - U.S.-based hedge fund Elliott Associates on Tuesday urged a London court to overturn a verdict supporting the London Metal Exchange's (LME) cancellation of nickel trades partly because the exchange failed to disclose documents.

The LME annulled $12 billion in nickel trades in March 2022 when prices shot to records above $100,000 a metric ton in a few hours of chaotic trade.

Elliott and market maker Jane Street Global Trading subsequently brought a case demanded a combined $472 million in compensation, alleging at a trial in June last year that the 146-year-old exchange had acted unlawfully.

London's High Court ruled last November that the LME had the right to cancel the trades because of exceptional circumstances, and was not obligated to consult market players prior to its decision.

Lawyers for Elliott told London's Court of Appeal that the LME belatedly released documents in May this year detailing its "Kill Switch" and "Trade Halt" internal procedures. It also newly disclosed an internal report that Elliott said detailed conflicts of interest at the exchange.

"The documents are highly material to the original claim and should have been provided prior to the first instance trial pursuant to the duty of candour," Elliott lawyers said in a document prepared for this week's hearings. Jane Street did not appeal the ruling.

The LME had previously said it had both the power and a duty to unwind the trades because a record $20 billion in margin calls could have led to at least seven clearing members defaulting, systemic risk and a potential "death spiral".

Court documents filed by the LME for the hearing were not immediately available, but the LME has previously said the appeal is without merit and that it would contest it vigorously.

Elliott reiterated many of its original arguments, saying that the ruling diluted protection provided by the Human Rights Act and also wrongly concluded the LME had the power to cancel the trades.

It said LME CEO Matthew Chamberlain had acted irrationally and did not have all the information needed to make a proper decision.

"Mr Chamberlain’s evidence... indicates that he himself was unclear as to the ambit of the powers available to the LME," Elliott's appeal document said.

"The content of the Kill Switch Procedures was materially relevant, and ought to have been taken into account."

The LME website says: "LME or member risk managers can enact the kill switch to either pull orders and prevent trading activity or prevent order submission".

An LME-commissioned internal report by consultancy Duff & Phelps cited "the inherent conflicts between the LME’s own interests and its regulatory obligations", Elliott said.

The LME, the world's largest metals marketplace, is owned by Hong Kong Exchanges and Clearing Ltd. (Reporting by Eric Onstad; Additional reporting by Pratima Desai; Editing by Jan Harvey)