I clocked up 5 hours there in the 2 days I visited that shop. I went on to purchase my entire 20kg luggage allowance for the flight home from Mega City's fan-friendly shelves! That's right, Mega City sells comics by the kilo! Great shop. Stood out like a fanboy oasis compared to the generally over-priced inner-city London comic vendors.
One notable exception is Orbital Comics, in the city-centre. The 'more-than-a-shop' features an art gallery which I didn't fully assess as I was too busy with my head in the comic bins. Friendly staff and a good deal on back issues. If it's toys you want, then head to Forbidden Planet on Shaftesbury Street. Although it boasts a a well-stocked basement full of Graphic Novels and some dvds, it's clearly the street-level floor jam-packed with toys, models and paraphernalia which keeps the doors open on this fairly large store. And there was Gosh! comics which was busy and eclectic, and Comicana, which would be a collector's haven if not for prices that reach for rewards far beyond market value.