I'm a multi fuel user, A Primus OmniLite Ti. What drew me to this stove was it's weight and no conversion is needed to run gas from liquid fuel, other than to purge the stove. Do not forget a funnel if you want refill at a petrol Pump or Jerry can.
Unmanned Petrol stations at some supermarkets would be a good bet, usually card only payments. Unfortunately 2 liters is the minimum delivery at most UK pumps from what I have seen. Keep an eye open for a building site and tradesmen, they may be using a small generator.
DIY shops have good supplies too, paraffin and gas. The webber canister came from B&Q, the slim Go systems came from Wicks, photo below. Screwfix, Toolstation, Homebace, the list almost endless.You can use Campingaz CP250 Gas Cartridge available at most supermarkets in the uk with an adapter.
HEAR There are plenty of Outdoor shops in the UK so there is not much chance of running out of a liquid fuel or gas. I alway carry Gas and Petrol, when on tour or Kayaking. Gas is by far the quickest way for a hot brew and I tend to use gas just for that purpose. In July this year I used 300ml of liquid fuel on a 6 day trip, cooking Breakfast and Dinner and half a canister of Weber gas brewing up at lunchtime. The go systems works well in bottle cage.
And if you totally run out there is always a small wood fire! or McDonalds
Andy
P.S No need to cook salad