What is the meaning of an amber traffic light (with no accompanying red light)?

Explanation: As you approach traffic lights that have been on green for some time, anticipate that they'll soon change. Check your mirror so that you know what traffic is behind you and how far away it is. If the lights change to steady amber, you should stop behind the stop line. If you're so close to the stop line when the lights change that to stop may cause a collision, you should continue. You'll only know the risk from traffic behind if you use your mirrors as you approach the lights.

Category: Band 2 traffic signs and signals (2021)

References: Highway Code: Page 102, Know Your Traffic Signs: Page 119