I am looking to trial making some Sauerkraut at home. I have been recommended getting canning salt. Trouble is the only available source is too much, at too high a price.
What other salts, readily available in the UK, would be suitable?
Any salt will work just fine, salt is salt. But salt that has had iodine added (table salt) can result in a brine with a cloudy texture. Some might consider this less aesthetically pleasing.
Further research indicates that while iodine can cause some problems, other impurities can cause further problems:
Salt for pickling:
For pickling any variety of common salt is suitable as long as it is pure. Impurities or additives can cause problems. Salt with chemicals to reduce caking should not be used as they make the brine cloudy. Salt with lime impurities can reduce the acidity of the final product and reduce the shelf life of the product. Salt with iron impurities can result in the blackening of the vegetables. Magnesium impurities impart a bitter taste. Carbonates can result in pickles with a soft texture (Lal, Siddappa and Tandon, 1986).
So in summary look for a high concentration of Sodium-chloride (NaCl) vs other ingredients. As another answer states, it seems kosher salt is an excellent, reasonably priced choice.
I typically use kosher salt. You could use sea salt as well. It is not necessary to use canning salt.
Probably in the "too much quantity" category though the price is generally quite low (especially on a per pound or kilo basis), water softener salt can be a good source of clean salt if you avoid the versions with any additives. I discovered it when I needed to maintain a water softener for a while and then noticed that it was a lot cleaner, more available year round, and oddly often cheaper than rock salt, so my ice-cream-maker salt is now a bucket of water softener salt. It is coarse and would take longer to dissolve unless you crushed it more.