They seem to be formed over the North Sea as they get more dispersed as the head over Eastern England.
If you work on the assumption that a new contrail will be a lot tighter and better defined than an old contrail which has been subjected to the wind, then the contrails over the North Sea are a lot tighter (like a sharp pencil) than those over Essex / Sussex (like a smudged charcoal line).
If that were the case, it would suggest the contrails originated overland with the latest contrails at the time of imaging being over the North Sea i.e a SW-NE track.
However, I think the image was taken on 15 Apr 1993 if its the same one as I found on another old thread. That one looked like EO / false colour where as this one is a radar image, so I can't be 100% certain.