Aside from the shipping
to UK question, you need to be aware of a couple of things when using a "car adapter" with a laptop.
1. Laptops use a fair amount of power. Many draw as much as 65 or 70 watts (say, 5 or 6 amps @ 12VDC). They can draw down your house batteries at about the same rate as electric refrigeration
2. Most car adapters are made to function in a vehicle, and one which is running. Voltage in a vehicle is usually 13.8 or higher. Many adapters will not charge your laptop batteries when connected to the typical 12V battery bank on a sailboat, unless the engine
Typically, they will run your laptop OK as the voltage drops below 13.5 or so, but they won't charge your batteries. Indeed, the batteries will be drained.
I've tested a number of these, including ones from IBM. Finally found a source of extremely well made adapters which, if you so specify, can work well down to about 10.5 or 11 volts input. These are from Lind Electronics
I bought two of them and they have worked extremely well, even with low voltage.
I don't know if they ship overseas or not, but I'd bet they do. It might be worthwhile to send them an email
enquiry and ask about shipping
outside the U.S. They will need the specifics on your laptop: brand, model #, etc. You also need to specify that this is for use on a small sailboat where voltages often are in the low 12s or even less, so you want an adapter which will charge the batteries even with that low voltage.
S/V Born Free