lol, nice to "hear" a local accent hehe.
Ive worked out what the sodaStream website means when it says a 60L bottle - it MAKES up to 60L of their fizzy drink.
Absolutely no where (that I can find) on their site does it actually tell you how big the bottle is... but on another website I found some guys mentioning it was about 400g so as you say, much smaller than a fire extinguisher.
Think I will stick with the FE route for now.
As for filling - you can get them done at BOC gases (right beside Exotic Aquatics!) for £7.
Ned Thompson is the man is ask for on that one.
HTH.
Andrew.