With regards to A/C it can (and usually is) something more expensive. But first. check that your system is still pressurized. When the pressure drops too low the compressor will not run to protect it from burning out/siezing. Check to see if the A/C clutch is engaging steady, on& off cycling or not on at all. Cycling on and off is common when the pressure Freon level drops too low.
Let us know what you find & we might be able to help better. Can't recall if the UK cars run the A/C with the Defog on, but the US cars do. It's an easy way to check the system when the outside temp is below 10'C
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