Cat will be safe from gas fire so run gas fire 24/7 and worry about bill later. House should stabilise at at least 16 degrees which is not hazardous and indeed the minimum workplace temparature under the Shops Offices and Factories Act (or at least it was when I last looked).

Borrow a sleeping bag. When not in bed, sit in sleeping bag near gas fire. When in bed, sleep in sleeping bag with duvet wrapped round the lot.

Wash sleeping bag before giving back.

Go to folk club, pick up heating engineer. He will keep you warm (nudge, nudge) until he is obligated enough to fix heating free!