LONDON (AP) — Britain's Treasury chief is warning that leaving the European Union without a deal would damage the economy and ultimately risk the break-up of the United Kingdom.

Philip Hammond is expected to use a showcase annual speech in the City of London on Thursday to warn contenders for the Conservative Party leadership that a no-deal Brexit could "risk the union and our economic prosperity."

According to excerpts from his speech, Hammond will say the contenders need to spell out what will happen if their Brexit plans falter, and outline what Plan B might be.

In a possible suggestion to a second referendum, Hammond will say that "if the new prime minister cannot end the deadlock in Parliament, then he will have to explore other democratic mechanisms to break the impasse."