Thank you all!
Yes its a 31 key and meets nicx66 description: From the one picture it appears to be one of lachenal's middle to high quality anglo concertinas (gold tooling, six fold bellows, ebony(ized) frames and handles, metal ends "framed" by the ebony trim.
The metal detailing is similar to the 20 key picture from mike byrne but not quite the same. I will take and post more pictures.
And yes- I have now looked more closely at the original beach photo and I dont think its the same one! I scanned it, enlarged it till the pixels showed and studied it carefully- its not the same! Pity really. However Granddad could play anything he picked up, so I am not surprised. I am fairly certain the one I have is the only one he owned in my lifetime (born 1949, he died in 72). I have been trying to date the picture, with help from my new wife. The costumes are somewhere 1900-1920s, and the hairstyles 1920s. I have created a family database and, if the girl under the concertina is my mum, and if she is 11 ???? That would make the picture 1925 (ish!!!)
Also: Thank you Robin Harrison and Stephen Chambers. I dont know exactly what he played on the prom, but he was a "real character". He liked comedy records (scznozzle Durante etc) and probably played jazz and folk. I intend to emulate him when I get good enough. At present I just sit in the garden and annoy the neighbours.....
Thank you all!!!