Thanks everyone for you helpful comments! I did initially test on pine but subsequently oak with similar clogging effect. The wedge is in very good condition and shaped to fine point so it couldn’t be this.

I went back and put a much keener edge on the blade ( other moulding planes i have seem to be more forgiving with less of an edge). I also reviewed the body again and found that lengthwise there was still a very slight concave profile , ie the blade mouth lay above the ends of the body, no doubt through wear. As a result it needed a slighter deeper setting to make a start the cut which rapidly became too deep as the plane body advanced. As the plane was a simple hollowing profile, I shaped something similar in reverse in wood ( sadly i don’t have the reverse moulding plane) lined it with sandpaper and took of some of the surface. This helped immensely. Combining it with a much sharper blade, suddenly i had ribbon shavings. The amount i had to remove was minuscule. It’s amazing how sensitive and finicky such a simple tool could be, but with a little attention probably performing as good as the day it was made.

Thanks again for all your pointers,

Regards,

Chris