So today it was a pleasant surprise to receive an even better image from Dr Paul Evans of Cardiff University. Paul can be reached here: EvansPS3@cardiff.ac.uk
He has kindly offered to make the data files for this new high-res image available to anybody who may be interested.
Here is the new image:
The trench is a real puzzle -- it is most unusual to find a trench or canyon of this type which is closed at both ends. The excavation of the trench cannot be laid simply at the door of tidal scour. And glacial erosion in this situation is not all that likely either, given that the prevailing direction of ice movement in both the Anglian and Devensian glaciations is most likely to have been perpendicular to the alignment of the trench, and not parallel with it. So there must be some structural influences at play. An interesting geomorphological enigma.