I'm pretty sure Halon and it's derivatives (And BCF) will not be available in the UK
Our aircraft firefighters at work are not even allowed to train with it as it depletes ozone rather effectively, but they do carry it as it's so effective.
Dry powder is good as you can clean it up more easily should your firefight be successful, the foams can be corrosive.
Don't use one into the wind though... I can attest for that...
Also they have a certain rapid effect on the digestive system should you ingest any... I can attest to that too...
Another option would be Fireflex its a permanently installed plastic pipe pressurised with foam that ruptures when it burns and sprays directly onto the source of the heat.
Had a search but it seems to be hard to find, I wonder if they are still available?
http://www.vwheritage.com/vw_spares_Fireflex-extinguish-0-5kg-FLAT-With-4m-trace-tube-AC999E0540L_act_shop.product_pID_160614_lang_EN_country_GB.htm