Hello Rob,
This decanter has never been conclusively attributed to any manufacturer or designer. In some instances it has been suggested that it is by James Powell & Sons, however this has not been based on any documentation. To date there have been no archive documents showing it as Powell, or indeed Walsh Walsh.
Loosely, it is likely to be a Stourbridge company based on its style. Those companies include, Richardsons, Thomas Webb, Stuart & Sons, but given a recent find by me that was marked Webb Corbett, we cannot now omit them!!
Oh, if you're thinking that these would have been marked, it is likely that this design would have been pre back-stamps.
Nigel