A single sign or signal can display advice, restrictions and warnings for all lanes.
Lane specific signs and signals can display advice, restrictions and warnings that apply to individual lanes.
Advice, not law. This rule is not written in capitals, so breaking it is not an offence in itself — but it can still be used in evidence in court to establish liability. The rules that say MUST or MUST NOT are the ones backed by law.
1 theory test question on this rule
From the DVSA revision question bank. These are not the questions asked in the real theory test. Each one shows the answer, the explanation, and our own note on why every other option is not it.