Outside built-up areas, what gap must a vehicle over 3,500 kg PTAC or longer than 7 metres leave in front of it, and why?

1. At least 50 metres, so that a car overtaking it can pull back in safely ahead of it
2. At least 5 metres, so that the driver can see the vehicle in front over the bonnet
3. At least 10 metres, so that the trailer clears the junction when stopping
4. At least 200 metres, so that dust from the vehicle in front settles