Scotland Yard / Great Wall in BTS - question

I've started a game with Egypt and used the chariots to eliminate England and take their 2 cities very early in the game.

In London, I have inherited the Great Wall and Scotland Yard (2 wonders I avoid).

Does the Great Wall now cover my boundaries or just England's at the point the wonder was created?

I'm also new to espionage and want to know in BTS, what are the advantages in Scotland Yard?

All your land, including the captured English land.

Oh also...there seems to be no advantage to me with SY now, as I seem to be able to produce spies without ever having to build it...

Scotland Yard gives you a 100% bonus to Espionage Points generated in that city. I don't generally build it either, but if you prioritize espionage-producing buildings in that city and perhaps settle any Great Spies your new Wall gets you, you'll outstrip the AI on espionage production early and easily.

In order for your spies (which anyone can build after they discover the Alphabet) to do anything they need to spend espionage points that you have built up vs the target civ.

Scotland Yard is to Espionage Points as the Academy is to Beakers. The Academy can only be built (1 per city) by a Great Scientist; Scotland Yard can only be built (1 per city) by a Great Spy. Scotland Yard increases the number of Espionage Points generated by that city by +100%.

i usually settle the first Great Spy, build Scotland Yard with the Second one, and settle all other Great Spies in that city.

The GW only works for the continent and water doesn't count.