Thought it may be worth a mention.
If you are using "bottled CO2" You can also use

Yes, carbon dioxide fire extinguishers. You can get them on
ebay for ?5 - ?15
second hand. (I suggest you don't pay more than ?15 for one)
If you were wondering why one is black the other is red, they are both "The same" (2kg) except for age. Since 1997 all fire extinguishers have to be red, so if some one is telling you theirs is new and its black, its at least 14 years old.