I don't know. There's two ways of looking at it. Maybe some makers will have a "fire sale" of stock to dispose of it while there is still a market. The other view is that maybe some producers will wind down or go out of business?
Which then may cause prices to rise? My own opinion is that most all lead bullets in Great Britain are used in carbines anyway and such carbines are used either on indoor ranges or outdoor ranges where recovery of the fired bullets is able to be done in compliance with the proposed restrictions.
Northern Ireland of course (where pistols are still lawful for target shooting just as the Channel Islands and Isle of Man) will be under whatever the EU decides and my gut feeling is that the EU will reject a ban. As their shooting lobby is far more effective than the near supine BASC.