Carnival is under renewed pressure to sweeten its offer for P&O Princess Cruises now that support among Princess' shareholders for a merger with Royal Caribbean has risen above 7.5%.

Jupiter Asset Management, one of Princess' largest shareholders with 3.5%, has been joined by another key institutional investor - who declined to be named - in backing a merger with Royal Caribbean. Princess, the world's third largest cruise operator, is also the target of a hostile takeover by Carnival, its biggest competitor. Carnival's offer values the company at around £3.2bn (€5.2bn), or 450p per share, in a mixture of cash and shares.