A lovely rifle. Shame it can't speak! There are quite a lot of case law bits and bobs regarding the legality of relic rifles, and it has been held on quite a few occasions, that a rifle that is in such a state (as in dug rusted relics like this), is incapable of discharging a missile, thus falling outside of the sec 1 firearms legislation. However, as stated, this is case law and depends on the judge on the day, so if you go in front of a judge who has a bad hangover and has had a domestic with his wife that morning, you would be found guilty of possessing a sec 1 firearm without a licence.
Best not complicate things really and seek advice. Firearms law has really tightened over the last few years. That's my opinion anyway