You may remember my saying that we had new neighbours and that they had a cat. A big ginger bruiser, by all accounts. We've seen him out and about a few times, I've tried to make friends with him. To me, he seems skittish and afraid, wanting to come and be curious but scared of us, wanting fuss but at the same time not wanting to be touched.
This evening, when Jamie came home, this was the sight greeting us on the dining room windowsill:

As you can see, he is a similar size to Fidget, but where Fidg is all muscle and sinew, Potato is a little podgy and not as beefy.
Anyway, we were giving Fidget loads of fuss, then I decided to take the above photo. We both left Fidget in the living room, and went into the dining room to take the photo. Fidget obviously then realised that we were paying this other cat more attention than him, and he came flying in, leapt up onto the table and shoving his face in the face of the other cat (insomuch as its possible to do so, through a closed window). Potato jumped down into the alley, so Fidget runs round into the kitchen and starts making a huge fuss to be let out.
So we let him out. As Jamie said, its important for Fidget to be allowed to assert his dominance over the other cat in his own territory. Fidget immediately launched himself at Potato, who legged it up the fence to get away. Fidget didn't follow, instead choosing to return to the window and jump up, I guess checking to make sure the other cat hadn't scented it. Then he jumped up onto the wall, and ran down the wall towards the other cat. Who, deciding that discretion is the better part of valour, legged it down into his own alleyway.
Fidget started stalking up and down the wall, I guess deciding whether or not to jump down on top of the other cat. At which point I plucked him off the wall, and took him back inside.
There is a lot of noise coming from next door, I guess they have friends over or something. So I'm not sure if the cat was outside to get away from the noise, or if he was outside because they were too busy entertaining to remember to let him in.
Anyway, no harm done, ginger cat is more aware than this house is not his house, and Fidget is happy.