Good post and covers the issue so far. There is no proposal for a voluntary ban on lead rifle ammunition however and as clay shooting is not included in the voluntary ban it will be possible post voluntary ban to practice with your Alex Martin on clays. Which brings up the issue of whether you can clay shoot with lead only on designated clay ranges rather on farm land I suspect clay shooting with lead will be restricted to established clay shooting grounds.
Personally the announcement has caused me to rethink the purchase of any British two and a half inch chambered gun as all my purchases are hunted with and shooting bismuth regularly may be too expensive. I will also not be bidding on the 28 bore Alex Martin over and under in the Holts sale this March as I will be a bit cautious until I see how things develop .
It will be interesting to see if the voluntary ban announcement has any effect on the March Holts sale of small bore shotguns and two and a half inch chambered side by sides.