Rule 88 - The Highway Code

Manoeuvring. You should be aware of what is behind and to the sides before manoeuvring. Look behind you; use mirrors if they are fitted. When in traffic queues look out for pedestrians crossing between vehicles and vehicles emerging from junctions or changing lanes. Position yourself so that drivers in front can see you in their mirrors. Additionally, when filtering in slow-moving traffic, take care and keep your speed low.

Remember: Observation – Signal – Manoeuvre