Yes, it's an interesting subject, the native status of any particular species.There are many species in Britain that fall into this 'possible/probable' catagory, it is almost impossible to give a definitive answer to them all.
Despite having been an active BSBI member for nearly 40 years, and being well aware of the criteria which are used to decide whether a plant is thought to be native or not, I am inclined towards the 'probably native' side of the debate with regards to Gooseberry.
Much of the current work in this field has been done by Preston, Pearman & Dines 2002 during the work to compile the New Atlas of the British & Irish Flora.
As Pearman says in his paper in Watsonia:
http://www.watsonia.org.uk/Wats26p271.pdf
'We felt then that whilst it is difficult or even
impossible to attain certainty in the field of
origin, the issues were best served by setting
out as many of the facts and dealing with as
many of the facets as we could, and making a
judgement based on all of those, and in
repeating this same process, using the same
criteria, for all the species in question.
Obviously some criteria might be more
important than others, not only as a generality,
but for particular species, but that would only
become clear in discussion.'
So as he rightly says, in many cases, native status can only be a judgement.
But nevertheless, a fascinating subject.
Dorts.