In London, which fishmongers sell *true* sashimi quality fish?!

In London, which fishmongers sell *true* sashimi quality fish?

If you ask an English fishmonger if his fish is "sashimi grade" and can be eaten raw, he either demurs or else says "Yes, this fish is extremely fresh." Then if you ask, "Has it been frozen?" He says "No, it's extremely fresh."

Unfortunately, a certain kind of freezing is what makes fish "sashimi grade" and safe to eat raw, since the freezing process destroys dangerous parasites. (See http://tinyurl.com/2n3yfm and http://tinyurl.com/3y5mzh ). London fishmongers are pretty ignorant about sashimi.

In London, where can I buy tuna, salmon, and other fish that are safe to eat raw?