As a barometer of economic sentiment, few measures gain as much exposure as the FTSE 100. What is less widely known about the index, however, is that nearly half of the trading in its constituent stocks takes place not on the London Stock Exchange, which calculates and licenses the benchmark, but on alternative venues.

The index, which values the UK's most highly capitalised companies, represents one of the last bastions of exchange dominance and is set to form the next battleground between incumbent markets and rival venues. That fight could be worth revenues of up to £185m, equal to a third of the LSE's income.