I think you'd definitely describe Aston as close knit. There's only around 7000 students here and everything is on one small campus which takes you about 5 minutes to walk from one side to the other!
I think you'd have different experiences at a 'close knit' uni to a bigger one. Like at Aston more often than not whilst walking across campus you'll meet at least 1/2 people that you know and you'll see the same people around even if you don't know them. I think it's nice because you don't feel like you're just another face in a huge sea of students. At a bigger, more spread out uni I think you'd have the opportunity to meet far more people but you'd probably see less of them just wandering around uni, if you see what I mean.