Update, the A class has no relays for exterior lights, it is all handled by the light switch.
I ended up fitting a new switch, which has got dip and main beam working again,but..
The parking lights [which worked ok when I bought the car] stopped working some time ago, I had hoped that the new switch would cure this as well but they still do not work.
As far as I can tell, if the side lights work then so should the parking lights. I have put a continuity meter across the new switch and have got continuity for sidelights/dip/front fog/rear fog. But no continuity across the switch for left or right parking lights.
Any ideas, please,as I would like to get my parking lights working again!