@Tinyroo all the answers are in the drone code ,its really easy to pass and it gives you the flyer ID that you need to fly it lasts for three years and at the moment its free
the operator ID lasts for a year from the date you register and right now costs £9 per year, the police have the power to ask for them and they can impose a fine if you fail to comply ,
you are really only going to be challenged if someone reports you to the police ,but that is a very rare thing ,the police are the only ones who have the power to ask you to produce your operator ID and flyer ID ,just because you have both of them does not mean you have cart blanche to fly anywhere you feel like ,you still have to observe local and CAA regulations where you intend to fly