Did it die along with the lights when you jumped the battery? Disconnect and isolate the negative battery cable for 5 minutes.

 

Didn't notice that the stereo wasn't working until after one or two further trips, BUT bought myself a multimeter from the local motorspares shop and tested the fuses.
some of them have no power running throught them regardless of whether or not the ignition is on and the ones with no power through them are NOT spares.
After all that I rechecked the stereo and lo and behold it now works even though I don't know what or how I did it !