XJ8 Key Fob stopped working?

[8potdave]

Pulled into work today, pressed the lock button and nothing! This has happened once or twice before but always started working again. However, when I returned to the car nothing again. I got in with the key and incidentally set the alarm off! Luckily I found that turning the ignition overrides the alarm so it stopped but I can't for the life of me get it going again. The fob is new, the previous owner replaced it last year and I've tried changing the battery. I also tried the whole reset thing that I found online but no response what so ever. Am baffled by this, any ideas?