Few outsiders have as much history with the London Stock Exchange Group as onetime investment banker Xavier Rolet. In 2005, while he was working for Lehman Brothers International (Europe) in London as co-head of global equity capital markets, Rolet became a senior relationship banker to the London Stock Exchange — and helped advise Clara Furse, the LSE’s then CEO, in the aftermath of a series of rapid-fire takeover bids from Deutsche Börse Group, Euronext, Macquarie Group and the Nasdaq Stock Market.

Now, as her successor, Rolet faces the challenge of trying to undo Furse’s chilly, combative legacy and strengthen the LSE’s competitive position by being more nimble and responsive to the banks and brokerage firms that constitute its core customers. He has no choice but to act quickly, because the LSE is losing ground to a new generation of rivals: high-speed, low-cost alternative trading venues...