Having now finished my degree and been given a shiny new Macbook Pro at work, I've no longer got a need for my trusty Air. It was the top end of the range when I bought it back in late 2011, so it has the 4GB of RAM and 128GB SSD. I had a three year warranty on it, and had it de-dusted by Apple a month or two back. All in good condition (think there's one tiny mark on the screen but will confirm) with box, charger (new about a year ago), paperwork and a corduroy case. The battery has gone through about 1100 cycles and 89.5% of design capacity battery (bloody good after three years of uni use)
I've upgraded it to Yosemite and have been having some trouble with the wifi since (Apple is apparently releasing an update soon), but there were no issues to report before that. I'll include the £25 ethernet adapter so you can use that for the time being instead.
Looking for £450 (halfway between Cex's buy and sell prices), and can meet you anywhere in zones 1 or 2 (I work in the City). Photos will follow soon.