The highway code states that the car must not be driven out of a gear at all times
Where?
122
Coasting. This term describes a vehicle travelling in neutral or with the clutch pressed down. It can reduce driver control because
- engine braking is eliminated
- vehicle speed downhill will increase quickly
- increased use of the footbrake can reduce its effectiveness
- steering response will be affected, particularly on bends and corners
- it may be more difficult to select the appropriate gear when needed
I see no MUST there, which is the convention used in the HC for representing a legal requirement.