Agreed. But that gun was not built in the Webley factory. Webley grip screws are a very fine thread and have a slightly raised head. The grip screws shown in the photographs are standard countersunk screws with a much coarser thread than I have ever seen on any Webley.
I am now firm in the belief It is a home built (or Saturday engineering shop ) Modification by someone reasonably proficient at engineering and at the time of modification, it was polished and refinished so all the parts match. I do have a full set of Guns Review bound volumes from 1968 until it ceased publication. I remember the article mentioned earlier and will dig them out. It will be interesting to compare serial numbers.