Thanks for your answer.
The other country is now more than twice my networth, perhaps I mis-calculated this in my previous post (it was just before I went to sleep) however I wouldn't normally make such a simple mistake. Regardless I am still confused.

I have games on 2 other servers. Trying to spy on a coutry > 2x my networth with both of us in GDI gives these results:

Express: Success. (Target is > 3x my networth)
Primary: Success.

If I try to spy on the leader in the Primary server (> 4x my networth) I get:
"Your forces will not spy on such a large opponent!"

But trying to spy the guy who just attacked me 9 times in the Tournament game gives me:
"GDI authority will not let you perform this operation without declaring war!"

The spy page states "The chance of success is related to both you and your targets ratio of Spies to Acres of Land", however it is unknown if this is the criteria for deciding if your spys will attempt an operation.

*All just normal vanilla "Spy" operations - not offensive

SO:
Why can I not attack back?
Why can I not spy?
Why did the other player not have to declare war before he attacked?
Why did the GDI still blocking me when the other player has already sent multiple attacks and offensive spy-ops at me?