Where can I buy kosher salt in London? I make a point of taking a few minutes to look around for the stuff whenever I go to a new supermarket / farmers market / ete etc and I haven't been able to find a source here. At the same time, I'm not wanting to import anything from the States, because it defeats the purpose of having a cheap supply of a goood salt.

Surely there is a place one can obtain Kosher salt in London, no?
You could try Maldon Sea Salt, or similar supermarket sea salts. While not identical to kosher salt, they can be used in a similar way. Maldon is also is much cheaper in the UK than it is in the US (where it's an import).

It's not a product I can recall seeing in many UK stores.