In standard Highway Code it is defined as a 2-seconds rule...

The two-second rule is a rule by which a driver may maintain a safe following distance at any speed. The rule is that a driver should ideally stay at least two seconds behind any vehicle that is directly in front of the driver's vehicle.
The practice has been shown to dramatically reduce risk of collision, and also the severity of an accident should an accident occur.

This is one of standards we were talking about earlier on.

Q: Is this rule are practised in here. How many drivers are actually have a clue of meaning of this?