Two varieties in ASDA tonight, both from the finest range (£2 per pack, 6 bangers per packet)

Cumberlands (small), 0.5g carb per 100g
and Gluten free, trace carb per 100g

Also worth a look is the finest range chorizo, you get 3 large chorizo, these are 1.5g carb per 100g, which is about 1.2g per chorizo. Very strong, very tasty.