Most of the famous names in the cast make token appearances. With Bill Oddie this is a merciful release (probably the most over-rated comedian ever), with Jimmy Tarbuck all too brief. The script is dreadful. I don't think it is its period (1967) just a sketch idea drawn out to a full length film. There is one good visual joke which is done by Roy Castle. Sykes has done much better stuff.
If you like slapstick, this is so funny. The trouble caused by one plank of wood is sometimes foreseeable, sometimes a surprise. It is ridiculous and daft. There is barely a script - very little dialogue at all. It's like a cartoon, only acted.
If you don't like slapstick, it's still worth trying. I live in a house with slapstick lovers and I think slapstick's a waste of time, but I still loved The Plank.