Travel company TUI AG warned of grounded vacation flights, Cambridge University said its supply of fee-paying continental European students could run dry. Corporate borrowers are stepping up efforts to avoid being caught off guard when Britain leaves the European Union (EU) next year.

Warnings about how Brexit might stop bond investors getting their money back are becoming lengthier, while clauses allowing issuers to switch governing jurisdiction away from English law are appearing in documentation. New courts to settle cross-border disputes are also opening in European capitals, a further sign of the looming threat to London's status as a financial hub.

British and EU negotiators are moving closer to a divorce deal. But there's still a risk that the financial institutions concentrated in London may find themselves isolated from their clients across a hastily constructed border. To head off the unthinkable, scores of lawyers, lobbyists, and bankers have been rewriting the debt-market rule books.