There are a number of different designs of L plate fixings available, as opposed to the traditional flat plastic plates that have been used for many years. Whilst the law doesn't specify how L plates must be attached to a vehicle, it does require that they must be displayed to the front and rear of a vehicle that's being driven by a learner and they must be the correct size – please see the link below:
Driver and Vehicle Standards Agency - L plates
L plates should be removed from a vehicle when it's not being used by a learner.
If you fail to display an L plate on your vehicle when you're learning to drive or if it's the wrong size, you can be fined and receive up to 6 penalty points on your driving licence.