Hi Dan,
I'm aware that this thread is about a month old, but could be useful to you or others considering a career at sea.
Shipping companies are continuously recruiting for new Officers and crew - Deck/engine Officers are in high demand so future prospects are good. However your post said that you're after a job in one of the onboard bars - just contact the appropriate shipping companies (e.g. P&O Ferries, Brittany Ferries, LD Lines, Seafrance, Wightlink, Red Funnel). ALL crew members who work on ships have to undergo a training programme, even if they are not directly responsible for the safety of the ship and it's passengers/other crew - some companies may pay for crew training.
Alternatively you could consider applying to a cruise line where you will benefit from unrivalled travel opportunities and a completely different lifestyle.
I for one have applied to start a sponsored degree and extensive training programme as a Deck Officer with a major cruise line - the course starts in September 2008 and I will hopefully be fully qualified within 3 years. Then you have the opportunity to rise on up through the ranks to Chief Officer and Captain.
If you really want a career at sea then you may prefer to take up one of these Deck (or Engine) positions; however to become a Ship's Officer you will be required to go through a lot of training and practical work experience. A career at sea (as an Officer or crew member) is not easy - the hours are long and if you work deep sea then you'll be away from your family/friends for extended periods of time. However, the working hours for crew operating on the English Channel are different - I believe it's something like 2 weeks on, 2 weeks off. But check this at the interview if you are offered one!
Good luck! :-)
James