macbook air wifi issue

My Macbook Air (late 2010) suddenly started dropping its wifi connection with my Time Capsule (2nd Gen) last night. At around the same time I had the same problem with my MacBook (late 2008). Both are running version 10.8.3. After a bit of research this morning I found that changing the service order under System Preferences>Network>Set Service Order - to put Bluetooth below Wifi in the priority order - seems to have cured the problem on the MacBook but not the MacBook Air.

There are no wifi issues that I am aware of with the iOS devices that I have - iPhone 4, iPhone 5 and iPad Mini.

Strange thing is that if I use Network Diagnostics to make the wifi connection on the MacBook Air and keep Network Diagnostics running in the background then the connection is held.

By coincidence, a couple of hours after this problem manifested itself, I had a warning on my Macbook that the hard drive on my Time Capsule was full and that it would start deleting the earliest backups. I use Time Machine on my MacBook but not on the MacBook Air. I'm not sure if this is just a coincidence or not but thought that I should mention it anyway. I've switched off Time Machine temporarily on my MacBook in the meantime.

There are some extremely long threads about wifi issues which offer a confusing amount of advice so I thought it better to start a fresh one.

I have reported the problem to Apple.

Any advice or guidance would be much appreciated.