Thank you NotSpaghetti! Luckygirl3, have looked up John Reilly - some beautiful work, similar, but so far can't find that picture.
The signature on the bottom was difficult to read, but I narrowed it down to Loys or Loyd. It has disappeared over the years, leaving a tide mark but as I said above, when I put the photo into AI, it immediately said the signature was Loys. (How did it do that??) So I definitely think it must be Christian Loys as previously suggested. The style seems consistent with the few images of his early work online. I bought it 20 plus years ago in Chatellailon-sur-Mer, near La Rochelle, so if he was roughly in that area a local poster shop might be happy to include it in their stock.