Typical, the identical scene recreated and saved out again now loads back in without problem (apart from taking a while to load) so appears to not be a consistent problem. The original scene still fails to load .

Just had a thought, I'd changed something between re-setting the scene. I'd de-selected 'use external binary morph targets'. Sure enough re-selecting this in general preferences, saving the scene and then re-loading causes the same crash, so it is a problem with 'use external binary morph targets' probably in conjunction with V4 in the scene.