I'm running into the same conduit doing my V/C job...though on the driver's side since I'm in the US, of course.

Isambard, did this advice help with your job? I followed the conduit and saw that it was connected to the alternator, but it seemed to split into a T with one arm going to the alternator, the other up over the valve cover, and a third heading somewhere down the block where I was unable to see (starter perhaps?).

I didn't want to deal with unbolting it from the alternator only to find out that doing so wouldn't provide me enough slack to remove the valve cover. Also because I'd already spent about 7 hours working on the passenger side and removing the coils and all the bolts/nuts on the driver side and putting it all back together seemed like less effort than making a guess, being wrong, and then putting it all back together.