I thought it was Jewish. so does the Observer.

From the Observer, online.

"In 1860 a Jewish immigrant from Eastern Europe called Joseph Malin opened the first business in London's East End selling fried fish alongside chipped potatoes which, until then, had been found only in the Irish potato shops. In 1968 the National Federation of Fish Fryers even presented a commemorative plaque to Malin's of Bow, recognising their founding role in the chippie business."

Apparently, the fried fish was originally brought by Portuguese Jews expelled from Portugal.

Penny