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Highway Code · Rule 121

Highway Code Rule 121

General rules, techniques and advice for all drivers and riders (103 to 158). Advisory guidance you are expected to follow.

  • General rules, techniques and advice for all drivers and riders
  • Advisory rule
  • OGL v3.0

What the rule says

Advisory

Rule 121 (Control of the vehicle (rules 117 to 126)) Brakes affected by water. If you have driven through deep water your brakes may be less effective. Test them at the first safe opportunity by pushing gently on the brake pedal to make sure that they work. If they are not fully effective, gently apply light pressure while driving slowly. This will help to dry them out.

Rule text reproduced verbatim from the official Highway Code (Crown copyright) under the Open Government Licence v3.0, see the attribution at the foot of this page.

In plain English

Stripped of the formal wording, Rule 121 comes down to one idea: rule 121 (Control of the vehicle (rules 117 to 126)) Brakes affected by water. It is advice rather than law, but examiners and the courts still treat it as the expected standard of safe driving.

It belongs to the general rules, techniques and advice for all drivers and riders part of the Code, the habits a confident, considerate driver builds until they are automatic. The aim is not to memorise the sentence word for word, but to understand the hazard it protects you from, so you apply it without having to think when it counts.

If you are learning, treat this rule as one piece of a connected set rather than an isolated fact. The related rules below sit in the same section and reinforce each other, reading them together is how the general rules, techniques and advice for all drivers and riders part of the Code starts to feel like common sense rather than a list to revise.

Because this is advisory rather than legal, no one will fine you for the rule alone, but ignoring it can still count against you in a careless-driving case, and it will cost you faults on the test. Either way, the safe move is to build the habit early, while a driving instructor can correct it, rather than relearning it under test pressure. That is exactly what the practice routes and coaching in the DriveRoutes app are designed to help with, turning the rules below into the way you naturally drive.

Why rule 121 matters on the road

These are the foundations every other skill builds on. Solid mirror work, sensible speed and good lighting habits quietly prevent the situations the rest of the Code has to deal with.

Common faults examiners record

In the general rules, techniques and advice for all drivers and riders part of the Code, the faults most often written on the marking sheet tend to be the same handful. Knowing them in advance is the quickest way to drive them out of your own habits:

  • Skipping or rushing mirror checks before a manoeuvre.
  • Carrying an unsuitable speed for the road and conditions.
  • Reacting late because hazards were spotted too close.

On the day

On the day, applying Rule 121 is about doing the safe, deliberate thing slightly earlier than feels necessary: read the situation in good time, observe fully, and act smoothly. The examiner is looking for planned driving, not perfection, and good habits formed in lessons carry you through.

Quick checklist

  • Read the situation early and plan your response.
  • Observe fully before you commit to anything.
  • Keep your speed suitable for the road and conditions.

More from General rules, techniques and advice for all drivers and riders

Related Highway Code rules

Rule 121, your questions

Rule 121 (Control of the vehicle (rules 117 to 126)) Brakes affected by water. It is advisory guidance rather than law, but you are still expected to follow it and an examiner can mark a fault if you do not.

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