Mercedes 'passed' it's mot yesterday, had service at the same time,nothing major just new pads and discs. So far so good, the lights are on all the time but when I tried the main beam nothing happened, a light on the dash (not the blue one) said they were on but they weren't, occassionally they would come on but didn't after dipping, on one occassion they came on but went off when turning a corner this suggested a dodgy connection. When I got home and opened the door none of the internal lights come on, can't see what would link the two.
I'm taking it back but wouldn't have a clue where to start.

Seems the 'auto' light sensor failure may be the issue, simple switch to manual seems to have sorted it. don't get these problems with a coop!

Well-sleuthed, easy fix!