What are the rules in the UK, when it comes to flying in built up areas. Do the rules apply where you have to fly 50meters away from building, or is the Mavric Mini exempt from this as it weighs 250g
The rules still apply I’m afraid. The sub-250g only exempts you from registering with the CAA. You should still stick to the drone code.
Guessing the means I can’t fly it in my garden
It might be worth getting in touch with your immediate neighbours and letting them know that you might be ‘practicing’ with your drone in the garden and will not wander in to theirs or go too high.
If they don’t mind then they wont dob you in to anyone.