Wooden Flap for identification

Another chap at Flying Legends passed me some photos of a wooden flap that he has.

It is about 9/10 foot long.

Can anyone assist him in identifying it ?

The flap is of a plywood construction with the following markings

WF3 1102 AND

ISS1
DD2/19

then

003/29/S/
NF3 MO4ND

DID 610

Thanks for your assistance.