Thought this might be useful as a quick way to check your tyres.
Simply place a 20p coin into the main tread grooves of your tyre. If the outer band of the 20p coin is obscured when it is inserted, then your tread is above the legal limit.
If the outer band of the coin is visible, then your tyres may be illegal and unsafe and should be checked immediately by a qualified tyre professional.
When taking the test, remember to check at least three locations around each tyre.
As the test is so quick and easy, stay safe by checking your tyres at least once a month.