En-Thrall-U

Little-known British brand of wooden jigsaw puzzles, thought to be of c1930's manufacture.
The few examples I have seen have all been fully interlocking in style.
Some examples have been found with the following printed on the box-base:
"Produced by R.W. Hall", whilst one past auction record for a 1000 piece puzzle, carried label information referencing R.W. Hall Ltd., Banstead, Surrey.