[CosmoK]

So, could Jan (or Yan) Svensson be an aka for Serge Jacques?

Since the moment I spotted the same pictorials you mention, Svensson was rated with a "very high probability" in my list of Jacques' aliases.

Don't have further clue about Basil Crawford-Smith, however, I have been told that when working in London, Jacques had some fun tricking publishers using aliases. For example, he asked Claudie Perrin to embody the photographer Sarah Joyce at the time he was using this alias for his own work. That "mystification", intended to help him opening some doors for business purpose, seems to have succeeded to a certain point.

That is to say that I won't be surprised at all to know that Jacques used one or more typical British names for alias during the time he worked in England (and maybe even after).