REUTERS/Fabian BimmerLONDON, Sept 22 (Reuters) - A temporary brake on gas and electricity derivatives when prices spike could improve the overall functioning of the energy market, the European Union's securities watchdog proposed on Thursday. "It would, therefore, appear useful to consider implementing, on a temporary basis and for energy derivative markets only, a new type of trading halt mechanism," ESMA said in a statement. Such a mechanism would need to be implemented as part of emergency measures tackling the current energy crisis, it added. Energy firms sell their output using derivatives markets, requiring them to post "margin" in the form of cash, in practice, to cover positions at clearing houses in case they turn sour. ESMA said such conditions include a time limit on their use, such as for the winter period when stresses in energy markets are expected to continue.

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