* EBA says banks should still implement guidance * EBA says won’t stop issuing guidance to banks * Lawyers say court backing could have wider impact (Adds French Banking Federation reaction) LONDON, April 15 (Reuters) - The European Union banking watchdog’s guidance to lenders on retail products should be declared invalid, an adviser to the EU’s top court said on Thursday, raising questions about financial supervision in the bloc. The European Banking Authority (EBA), which coordinates how EU banking laws are applied across the 27 EU states, had issued non-legally binding guidance on the supervision and governance of retail banking products. Such “soft law” guidance, also widely used by the bloc’s separate insurance and securities watchdogs, sets out how an EU law should be implemented in practice to ensure consistency across the bloc.