After some research I would say my site have been hit by an EMD penalty, it seems many other people have faced the same.
It would be very useful to know how to deal with this, many topics discuss the reasons behind it, but few have a realistic response for fast action.
I am in two minds - one would be to try and improve content etc, but this is subjective and could take any amount of time, or never resolve the issue.
The other would be to move the content to a new URL, which poses the question, should I do a 301 redirect, or would this just transfer the penalty?
If no redirect, then I am proposing starting fresh - as the sites hit by EMD penalties are deemed 'low quality' this might be the fastest way to recovery.
If I move the old content to my established main site as a sub folder, would this cause any problems?
Many thanks for people responses.