Diana Model-8 Target.
This very rare pistol was otherwise known as "The Holborn" and the "Diana Target".
With many thanks to Lawrie for these excellent pics:
Thanks again to Lawrie for these pics, which show more detail of the rear sight.
There are also several that show a reproduction sight Lawrie made for an American collector.
With thanks to John M for these pics of the same pistol:
Diana Model-8 Target - Unbranded.
With thanks to John G for these pics.
This pistol was marketed in the UK as the 'Holborn' and the absence of a 'Diana' marking, as on the other mod 8 in this gallery, suggests it could have been left unbranded for export.