okay im a electrician so i will help you out pal, you would be better off with a multi meter but a neon screw driver will do. Dont bother with the volt stick as you will have to disconnect cables to get it to work properly.
Okay so nothing happend to make them go faulty ie putting up picture etc? If not it just sounds like a lose connection.
First drop both light fittings and with the power on and light switch turned on see if you have any power at either of the light fittings by touching it on the reds/browns.
If there is no light on the neon this means there is no power going to the light fitting thats working and drop it to look for a lose connection to re energize the lights that arent working.
If there is power at the light has one light got more cables say two black/blue 3 red/brown and 1 red/brown on its own and the other has 1 b/b 2 r/b 1 r/b the problem will most prob be at the one with more cables.
With the power switched of give all the cables a pull, hopefully one will just fall out and thats your problem. If all is tight in both i would do the same at your light switchs in case they where switch feed.
hope this helps. Dont think its vermine because it would be tripping all the time instead of not working
gd luck