Carnival may need to come up with a £500m show of intent, as well as an improved offer, if it is to enter into talks with the P&O Princess board, according to a report in The Times.

Carnival is trying to break up an agreed £4.9bn merger between Royal Caribbean and P&O. There were reports at the weekend that Carnival might have to put up a massive dowry, only to be returned if any formal offer for the British company is cleared by regulators.

The Times says P&O is convinced that Carnival, which has outlined a £3.2bn counter-offer, would never get clearance for its bid and fears the US group could simply be coming in with a spoiling tactic.

Officially, the terms of the P&O-Royal Caribbean deal do not allow the British company to solicit another offer, says The Times. P&O cannot therefore put a series of demands to Carnival to elicit an acceptable bid, such as the £500m upfront payment.

P&O is allowed to talk to a third party if it receives a superior and deliverable offer, but it must give Royal Caribbean 10 working days notice of such a development before opening discussions with that other party.