In an emergency.... I can assure you the last thing your going to worry about is the mess. Vacuuming power up is never going to be as bad as sitting next to burnt out shell.
Anyway… Fire extinguishers, if your lucky enough to get a special offer, go for it. Otherwise take a look at www.screwfix.com
Don't be tempted by cheap aerosol type fire extinguishers, go for something at least 1.5kg, make sure it also has a gauge. Its cheap, very cheap insurance and you'll only get one chance to save your pride and joy. Ideally buy two, one for the kitchen with a fire blanket, and another by the drivers seat.
Most of all, familiarise yourself with your extinguishing equipment and make sure everyone else in your 'party' is also aware of how to use the equipment as well. The last thing you want to do is read the instructions before putting out the fire. Literally every second counts.
Very slightly off topic, but just as relevant. And very sobering.
Some of you will now know I live in an isolated position with no neighbours close by. As soon as my daughter was old enough to talk, we taught her how to use the phone to call the emergency services and how to tell them how to get to our remote location (ordnance survey grid refs on bottom of the phone). Like a couple of my friends, some of you won't realise the need to teach a young child these basic instructions. What I didn't tell my friends was that I have a severe heart condition which could render me unconscious very quickly (sadly my younger brother died at the age of 40 because of the same condition - due to surgery I'm now fine.) so the calling of outside help was very important. But let me take this a stage further. What if you had an accident? Thousand do, every day, not one of them plan them. What if your busy sorting a fire out? Need I go on, I don't think so…
Take care everyone, and enjoy life