Shooting legal advice
Probably not assuming you bought the gun new. If the gun was new the law requires that it should be of merchantable quality and fit for purpose.

In my view a split stock would not be of merchantable quality so you are entitled either to have the stock replaced or to have a replacement gun if that is not possible.

The responsibility to do this lies with the retailer, not the importer, so you need to go back to the shop you bought it from and ask for a repair or replacement.

Any guarantee given by the manufacturer/importer is over and above your ordinary rights under consumer law and does not replace them.

All this assumes that the split was not the result of careless use. If it was then you have no redress.