I have had great success with WineSkin http://www.wineskin.net/

I purchased it in the US and they don't seem to have any UK retailers but something to think about when going back from the US, you can buy them in large BevMo! stores and many other places.

It forms a leak-proof seal around your bottle, so even if it gets broken it will only leak into the bag and not into the rest of your luggage. Perfect for red wine and other kinds of liquids you know will spoil lots of your luggage if broken.