The scheme gives even greater rewards to the company's existing base of loyal passengers and is totally free of charge.

Says a P&O Cruises spokesman: "One of the most exciting features of The Portunus Club is its tiered structure which lets us identify and reward customers according to their level of loyalty. This also means we can communicate with each customer segment separately, addressing the varying needs of each group."

Passengers automatically become members of The Portunus Club after their first cruise, and are awarded ten points for every night spent on board. Each member is allocated a tier based on their points total, and milestone gifts are awarded on reaching the next level. The three tiers are named Ruby, Sapphire and Gold, after the colours of the P&O Cruises flag.

The scheme offers a range of exclusive membership benefits, many of which do not have an equivalent financial value. These include priority embarkation, a dedicated check-in, a Loyalty Manager on board each cruise, welcome packages and invitations to special events such as an exclusive Senior Officer party.

Members also receive a discount against on board purchases, from five per cent for the Ruby Tier, seven point five per cent for the Sapphire Tier and ten per cent for Gold Tier members.