LONDON—A specialist London court will decide whether a long-awaited multi-billion pound class action against some of the world’s biggest banks over alleged foreign exchange rigging can proceed, after a five-day hearing kicked off on Monday. JPMorgan, Citigroup, Barclays, UBS, and NatWest, along with Japan’s MUFG Bank, are braced for the first forex class action in Britain over cartels dubbed “Essex Express” and “Three Way Banana Split.” The European Commission fined all the lenders apart from UBS, which had alerted the body to the two cartels, a total of more than 1 billion euros ($1.2 billion) over the matter in 2019. A similar decision by the Swiss regulator added a further 90 million Swiss francs ($98.49 million) in fines. Michael O’Higgins, the former chairman of British watchdog The Pensions Regulator, and Phillip Evans, a former inquiry chair at the Competition Markets Authority, are now vying to lead a class action case …