Carnival's attempt to upset P&O Princess Cruises' agreed merger with Royal Caribbean will depend on Henderson Global Investors and Merrill Lynch Investment Managers (MLIM), which together hold 10% of P&O Princess.

Carnival has said it will contact P&O Princess Cruises' shareholders directly this week. According to Citywatch, the largest shareholders after Henderson and MLIM are Franklin Templeton and M&G, each with 4%, followed by Barclays Global Investors, Jupiter, Oppenheimer, Axa Investment Managers and Legal & General, each with 3%.