Evening all from Estuary-Land. Horsetan, has the Citroen been retro-fitted with electronic ignition? If not check the vacuum tube between the inlet manifold and the distributor. This used to be a common problem with vacuum advance/retard, engines cutting out when not under load. This is often due to the vacuum tube becoming perished or collapsing. The ideal would be to fit electronic ignition, some for 'classic' cars is even made to look like the originals. I disposed of my classic vehicle some years ago when I had a sudden outbreak of reality, the new owner in that time has got little further than myself in getting it back on the road.