In the 1980s, Mrs Pat Midgley and other museum supporters rescued the sole-surviving fishermen's yard and cottages to survive wholesale post-war demolition of the North End.

The one-up one-down dwellings once occupied by families with as many as nine children are now a fascinating visitor attraction.

The chairman of the North End Trust, Dr Paul Richards, said: "We thought the smokehouses had all gone. North Enders remember one or two in the 1940s but there was so much demolition in 1958/59 we didn't think there was anything left."

He explained how an invoice found in the museum files started the trail by referring to a consignment of smoked herring for the Lamb pub in King Street, now the offices of solicitors Metcalfe, Copeman and Pettefar.

He said: "The delivery came from fishmonger Thomas Westwood. We knew his shop used to be at 3-5 St Anns Street and decided he must have had somewhere on the premises to smoke herring – but where the devil was it?"

There was one clue on the outside of the building in the form of two bricked-up openings. "They looked a bit odd and too small to be windows. We thought they could have housed the louvred shutters used to control the smoke," said Dr Richards.

The building had been altered for residential use in the 1970s but removing 20th century panels and taking out cupboards revealed signs of smoke indicating the location of the smokehouse. "It's quite clear where the preparation area was and I guess it was his three daughters who prepared the herring for smoking," Dr Richards went on.

One of the shutters was found intact behind some planks and, astonishingly, it was still in working order. Some parts remained of the second shutter and a replica can now be made to replace the missing section.

The hunt for historical traces goes on and Dr Richards said: "We think if we pull off the shop front fascia board we will see Thomas' name."

He believes that the unique appeal of all the fragments of a once-thriving industry and community now preserved in the museum may bring significant new recognition.

"What we are going to do is try to get the whole complex listed by English Heritage. Not because it is of great architectural merit but because of the story it tells. If it is listed, it will be nationally important as well as preserving the North End in a way we thought in the 1960s had certainly been lost forever," said Dr Richards.

Work on the new extension to the museum is due to start in September and the whole project could take three years to complete.

But Dr Richards hopes that in a year the buildings will be fully integrated, making the museum more comprehensive and enhancing its educational value and visitors' experience.

"We have preserved an important slice of Lynn's heritage. There has been a fishing community in this part of the town for a thousand years," he added.