Lights, number plates and accessories

• A lot of cars have their fog lights on when its not foggy, is it legal?
• Have you any tips for driving in the winter conditions / fog?
• How dark can I tint my windows?
• I have seen a car with blue neon lights under the vehicle, is it legal?
• I have seen cars with small blue lights on the windscreen wipers, is this legal?
• I have seen some cars with lights on its tyres, is it legal?
• I want to have a personalised numberplate with fancy writing, what are the requirements?
• If I tamper with my vehicle's number plate so it can't be read, is it illegal?
• Is it illegal to drive a car with a broken speedometer?