The purchase by of the plural version of its website shatters the previous record for a ".co.uk" domain name, which was set in October 2007 when venture capital firm ASAP Ventures acquired the domain Recycle.co.uk for £150,000.
The company is going to split content between the two cruise sites so that one is for deals and the plural version is for social networking.
will be used to create a cruise community with user-generated content.
The company is aiming to more than double the level of user-generated content by increasing online customer reviews, comments and information.
Cruise.co.uk launched a campaign earlier this month, which involved it buying 10,000 copies of the £16.99 Berlitz Cruise Guide to give away free to anyone posting a cruise review on its website.
Seamus Conlon, managing director of Cruise.co.uk, said: "'Cruises' is consistently ranked first on Google with 'cruise' just behind. We wanted the top positions so that when internet users are searching for cruise deals, reviews or news we are the first port of call."
Cruise.co.uk was formerly owned by Carnival Corporation, which owns P&O Cruises, Princess Cruises and Cunard Cruise Line, and was sold last year to its management team.
Top five highest prices for .co.uk domain names:
1. Cruises.co.uk, £560,000 -- purchased January 2008
2. Recycle.co.uk, £150,000 -- purchased October 2007
3. Ink.co.uk, £130,425 -- purchased in 2007
4. Mobile.co.uk, £120,000 -- purchased in 2007
5. Taste.co.uk, £110,000 -- purchased in 1997
World's most expensive domain names (USD):
1. Sex.com, $12m -- purchased in 2005
2. Porn.com, $9.5m -- purchased in 2007
3. Business.com, $7.5m -- purchased in 1999
4. Diamond.com, $7.5m -- purchased in 2006
5. Beer.com, $7m -- purchased in 1999