If medieval england was Isolated

Hello,
First of all, I'm sorry if this is really the wrong place to ask this, but I'm struggling to find other resources.
I was wandering if anyone on here could please help me with research on isolated countries by helping me with some questions:
Mainly, What would have happened to a Medieval European country, such as 14th century England. if it were completely Isolated from all outside contact (if it had no foreign trade, relations etc).
How would this isolation affect it (including it's development, economy etc)?
What struggles would it have had in it's self-reliance?
Thank you very much!