HELP! 320d Wipers failed in rain

[eigenmode]

After some torrential rain over the last few days the wipers stopped working on my 2011 320d M Sport. An auto-electrician couldn't find any issues with the car after a diagnostics scan, and the wipers started working again. They stopped again after some more rain, and I changed the wiper relay for a new one. This didn't fix it and I can't rely on it in this weather.
I have no idea what to look at next, does anyone have experience of this problem and, if so, how did you fix it?

Thanks.

Mike

[miniman]

My E39 used to do this - was the ignition switch.

[eigenmode]

Thanks for that, miniman. I don't know whether the scan would have included checking that. The car starts and drives OK, so what was fixed/replaced on yours?

Mike

[miniman]

Well on the E39 it was the physical electrical switch attached to the back of the ignition barrel, but looking at E90 it looks like they have completely different start/stop button arrangement so doubt it's the same issue.

[iSore]

Has it got rain sensing wipers?

[eigenmode]

No, it's not fitted with those. Mike

[iSore]

The relay is the normal thing on those. But you've changed it...........