This is a council house, tell them you need a visit due to serious concerns over the state of the building, or your health.
Councils went through a period of providing cavity wall and other insulations, they may visit and notice your issue pretty damned quickly! 'Energy efficiency' is the buzz-word of the day, lowering bills - saving the planet, all that; use this as your ammo. Really, you need to get a visit to your cold home, you pay them.
If they refuse I'd contact the CAB and see where you stand. Personally i'd borabard the council after the first visit refusal, then i'd inform them of your withholding council tax until they do visit (but bank the money so you can pay it).
Good luck.