[Mikeju53]

It seems I wrote too soon!

I've just checked the Putnam book "Saunders and Saro Aircraft since 1917" by Peter London.

In Appendix 2, the lists the Walrus and Sea Otter production by Saro, then in Appendix 3, there is a list of Saro plants during WW2.

Lo and behold, there are two possibilities listed. One of them is Weybridge Trading Estate, Addlestone. The second is The Chapel, Addlestone Road, Weybridge.

I hope this helps.