Interior lights not working

[kibondo22]

Hi all - does anyone have any suggestions why all my interior lights on vwt6.1 have stopped working, with exception of just two?

the photo shows the two lights that ARE working (the striplight in the kitchen unit and the single middle light above the hob).
none of the others turn on...

ive done a continuity test with a multimeter on all the fuses under the drivers seat and under the steering wheel (my van is LHD) and all are working ok.
that sadly has exhausted the extent of my electrical investigative abilities

thanks in advance for any other suggestions