You can find out more information through the NATS eAIP
If you are using software such as Altitude Angel, you may come across areas that are highlighted red and say that it is a restricted area. Even though it's classified as a restricted area, it may not be entirely restricted for Unmanned Aircraft specifically.
With a bit of know-how, you can find out more information to see if the Restricted or Hazardous areas affects all aviation or just specific types of aircraft such as Helicopters.
Here's a video of how to find out more information using the NATS eAIP.
If there is no other reason why you cannot fly your unmanned aircraft within a restricted area (because for example, it is only applicable to Helicopters) and there is a contact number, it would be polite to contact them to let them know when and where you will be and if they request, to notify them when you are landed.