London investors sent a message to Hong Kong Exchanges & Clearing on Wednesday: “Pull the other one – it’s got bells on”. That old British expression of disbelief was apparent in the feeble 5 per cent jump in the London Stock Exchange’s shares. HKEX hopes to buy LSE for an enterprise value of ￡31.6bn. If this was likely to succeed, shares should have jumped by the 23 per cent premium offered.

The world’s great bourses are national institutions, or at least civic ones. Takeovers and mergers typically fail for this reason. The bosses of exchange groups – whose real businesses these days are data, clearing and derivatives – should not fool themselves otherwise. Thanks to Brexit, the UK government is in chaos. Even so, it cannot meekly nod this takeover through.

HKEX is both too close to China and too divorced from it. As a big business based in a troubled autonomous territory, HKEX is more exposed to the hostility of the Chinese government than to its lucrative favour. The US may object to the deal on security grounds, even if the UK does not.