Having taken a window out yesterday and thrown away the trickle vent that was on it (no problem, I'll get a smart new one tomorrow) it seems that no-one sells them :(
I've done B&Q and Wickes without luck. Any ideas of source for plastic (pref) vents about 350-400mm by 35mm? I now have a window with a hole in the frame!
Cheers,
Darren