It was the year supersonic jet Concorde first entered service and Brotherhood of Man won the Eurovision Song Contest for Britain with Save Your Kisses for Me, but 1976 was also the year Zaks was formed.

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And to celebrate its 40th anniversary the Norfolk dining institution, which runs authentic American diners in Norwich, Poringland and Thetford, gave customers the chance to buy burgers at 1976 prices.

Huge queues gathered outside the Forum on Saturday as the company served up two of its biggest sellers at their original prices from a replica of the original Zaks caravan which used to sit on the site now occupied by the Vue Cinema, on Farmer's Avenue. rate

Customers were asked for a minimum donation of just 50p for a De-Luxe Burger and 56p for a Big Un & Cheese Burger at the one-off anniversary event with all food proceeds going to Zaks' official charity, Connects & Co which supports young carers.

Yvette Clements, 51, from Great Plumstead, was one of the many people who queued to get a burger and to remember old times.

She said: 'Its just like reminiscing for us really and hoping to bump into people we haven't seen for a few years.

'We used to go up on our motorbikes on a Sunday night – razz about the city, park up and have a burger. It was the place to be.'

Robert Meek, 43, from Lakenham, who has been a Zak's customer for more than 30 years, said: 'My parents used to go to the burger van on the top of the hill all those years ago.

'There's a lot more people than I thought. It's a chance to reminisce really.'

Chris Carr, chief operating officer at Zaks, said he was 'amazed' by just how many people had turned out for the event. He said: 'The love out there for Zaks has been phenomenal over the last 40 years and this is our way of saying thank you.'

The event also included baton twirling displays, the Norfolk Brawds roller derby team, retro American cars and live soul music.

Zaks' first Norwich restaurant, the Mousehold diner, opened in 1979. Zaks Waterside opened in 1988, followed by Poringland in 2005 and Thetford in 2015.