Many thanks for looking into this but because of the time delay between the UK and the west coast of the US I have had all day to really have a go at this. It turns out to be a simple "error" on my part. Not really an error but "it wasn't in the manual" so I didn't do it.
The problem stemmed from the fact of uploading two images (the 2nd being a thumbnail). In the DFP behaviour I inserted the default hiddenfile valuefor the main image but left this blank for the thumbnail. As this data was not being inserted into the database but merely uploaded to another folder, It didn't seem logical to me to have to give the thumbnail a default value.
Well the answer is that you do. By just placing the same default value in for the thumbnail as for the main image it stopped the database from being deleted.