You won't get shot down in the UK, there's not enough fields left for the bits to fall in......In the US you will probably be intercepted (your tax dollars at work!) and if you are doing something dodgey, ie. penetrating a MOA, loitering over a nuclear power plant etc,....and not responding to the F16 on your wing tip, you will more than likely be shot down. However if you were to stick to your filed flight plan, and / or RT failure procedures, and carry out interception procedures correctly, then you should be ok...