More than half of drivers in the UK would be shocked to discover that a seemingly innocent gesture behind the wheel is, in fact, off limits.

It’s something you might have already done today, or at least witnessed, and it could cost you £1,000.

And what is this big no-no? Flashing your lights. Yes, if you flash your lights for any reason outside of the Highway Code, you could end up with a fine of up to one grand, depending on the circumstances.

That means such friendly signals as letting a driver through, overtake, or a simple thank you, is off limits.

The exact wording of the Highway Code tells us that: “Flashing headlights. Only flash your headlights to let other road users know that you are there. Do not flash your headlights to convey any other message or intimidate other road users.”

Of course, you won't always be hit for the full amount for breaking the rules, and the fine varies depending on the particular offense, but there is one instance that is almost certain to land you in trouble if caught: flashing to warn other drivers about a speed camera.

If there’s a speed trap or other device used for monitoring speed ahead and you think it might be a good idea to warn a fellow motorist, think again.

This is just one of the things that drivers can overlook, with parking being another tricky area. For example, did you know that there are certain rules for parking on the street, and even more surrounding parking in a loading bay?