Cheats will head to Borough market by London Bridge tube where shop/stalls such as Applebee's and Mersea island's sell the freshest of the fresh Italian octopus and oysters, respectively. Otherwise, head to Billingsgate fish market (Poplar, E14), the largest in the UK. They sell everything imaginable at trade-ish prices. The only drawback are its opening hours – tuesday to saturday from 5.00am - 8.30.

Steve Hatt on The Essex Rd just up from the Angel Islington has some serious devotees and I think the foodhall in Selfridges on Oxford Street is very good if you are central. But you could also do a lot worse then the two excellent fish stalls at Borough Market (Furness being my personal favorite). Worth mentioning, although I am wary of supermarkets in general, is that Morrisons have won an award for their wet fish counters. The last time I visited one I bought some of the best squid I have eaten in a long time.