Straight answer is 70+ into the halal trade, of which alot os simply diced up or minced and sold into the Islamic market place - and alot is exported to the Islamic world - Simply put the traditional cooking methods for their cuisine suit mutton, IE Slow cooking in sauces - etc.
The remainder, often go into the catering trade in general - so think ready meal pies etc, where its sold as "shepherds pie" so its not a lie nto call it that.
Canteens etc.
Again a fair amount of this is exported.
The proportion will vary, with northern markets having a very high share going export and halal simply because of the larger halal-requiring population nearby, and links back to halal consuming country’s of origin facilitating the export market.