Rule 164
Large vehicles. Overtaking these is more difficult. You should drop back. This will increase your ability to see ahead and should allow the driver of the large vehicle to see you in their mirrors. Getting too close to large vehicles, including agricultural vehicles such as a tractor with a trailer or other fixed equipment, will obscure your view of the road ahead and there may be another slow-moving vehicle in front make sure that you have enough room to complete your overtaking manoeuvre before committing yourself. It takes longer to pass a large vehicle. If in doubt do not overtake not assume you can follow a vehicle ahead which is overtaking a long vehicle. If a problem develops, they may abort overtaking and pull back in Rule 164: Do not cut in too quickly