Just give us the type, not the registration. The interest is in which 2 seater you think flies that fast. It’s odd that your father is a new pilot, but is flying a very fast aircraft.
I presume your father understands best glide speed if he has a license, as you do not have a license, I understand why you find the concept confusing above.
What is REALLY odd is why your pilot father doesn’t explain the concept to you, understand what controlled airspace is, or know about SEP operations.
The funny thing is, if you just asked real questions, you’d get real answers from experienced pilots, it sounds like you’ve made something up though.
Now, back to the aircraft, tell us which mk Spitfire it is, because I’d say it’s less risk in an original TR9 if that’s what you have.