I see all the pub mechanics are out in force 🙂
Unless it’s below about -15degC, then the fuel should be fine. Waxing up basically refers to the wax content of diesel seperating/freezing up in extreme cold.
Glow plugs on HDi’s aren’t really necessary, and if they do fail, the worst that’ll happen is the engine will take a bit more cranking than normal before it fires up, and will smoke more upon start-up.
And the glow plugs work anytime the engine temperature is below 60degC IIRC, and continue to operate for upto 2 minutes after the engine has started (post-glow is used on most modern diesels to improve emmisions immediately after start-up).
As for what could be wrong with your car, given the symptoms, and the fact it’s gotten worse in the cold weather, it could possible be sticking injectors. If it’s sticking injectors, it’ll probably start with either a bump start (make sure you get the engine speed above the usual cranking speed), or a bit EasyStart/WD40/some flammable aerosol sprayed down it’s throat (take the boost hose of at the inlet manifold, and spray in just enough to get the engine to fire while cranking – spray in small doses until it fires, don’t just spray and hold as you’re likely to blow the engine up that way!)
If it doesn’t start with any of those methods, it’s likely to be an electrical fault.