Mixed load legal for wildfowling?

I’m told you can get cartridges with a mixed load of steel and bismuth shot. Would these be lawful for wildfowling in this country?

loaded over the top of steel. The aim is to combine the density of bismuth with the greater spread of steel shot. Both substances are lawful for shooting wildfowl and the fact they are combined in one cartridge makes no difference to their legality. David says: As far as I know, these are only made by Rottweil and consist of bismuth