LONDON • When Ms Laura Cha landed at Heathrow on Sept 5, she was ostensibly in town to see friends and family and to catch up with Mr Mark Tucker, the chairman of HSBC, on whose board she sits. But the US-educated executive was also on a secret mission, code-named Project Lima. As chairman of Hong Kong Exchanges and Clearing (HKEX), she and her chief executive Charles Li had requested a meeting with their opposite numbers at the London Stock Exchange (LSE).

Last Monday morning, they descended on the LSE's headquarters and in a 50-minute meeting, they dropped their bombshell. The HKEX wanted to buy the LSE for £32 billion (S$55 billion). If consummated, the deal would be among the year's top 10 mergers and acquisitions (M&A), and by far the biggest exchange takeover in history.