Sections from the Highway code:
175
You MUST stop behind the white ‘Stop’ line across your side of the road unless the light is green. If the amber light appears you may go on only if you have already crossed the stop line or are so close to it that to stop might cause a collision.
[Laws RTA 1988 sect 36 & TSRGD regs 10 & 36]
176
You MUST NOT move forward over the white line when the red light is showing. Only go forward when the traffic lights are green if there is room for you to clear the junction safely or you are taking up a position to turn right. If the traffic lights are not working, treat the situation as you would an unmarked junction and proceed with great care.
Turning left
182
Use your mirrors and give a left-turn signal well before you turn left. Do not overtake just before you turn left and watch out for traffic coming up on your left before you make the turn, especially if driving a large vehicle. Cyclists, motorcyclists and other road users in particular may be hidden from your view.
183
When turning
• keep as close to the left as is safe and practicable
• give way to any vehicles using a bus lane, cycle lane or tramway from either direction