The lots up for auction include an iconic movie script (minus a crucial plot spoiler), a mask that has terrified generations of sci-fi fans and even a chunk of a beloved starship.

More than 700 possessions of David Prowse, the Bristolian who played Darth Vader in the original Star Wars trilogy, are being sold off in his home city following his death aged 85 last year.

Included is his The Empire Strikes Back script, which has key lines removed to keep Vader’s relationship with Luke Skywalker secret, a piece of the Millennium Falcon’s cockpit and a Vader mask Prowse is believed to have used for appearances at conventions and events.

Appropriately, the collection will be sold on 4 May – a nod to the franchise’s famous line: “May the force be with you.”

Auctioneer Andrew Stowe, of East Bristol Auctions, said: ‘‘When I was rummaging through the boxes from his house, every now and then I’d come across something special and it would send my brain racing.

“In one box I’d find his Empire Strikes Back script, in another I found an actual piece of the Millennium Falcon, then a little deeper down I’d find a letter from Peter Cushing.”

The Empire Strikes Back script is expected to sell for thousands. ‘‘My spine tingled when I first saw the script,” said Stowe. But the line revealing Vader and Luke’s relationship does not feature.

Stowe said: “The reveal – perhaps the most recognised moment in cinema history – was kept a big secret from most of the cast. As Prowse’s lines would be over-dubbed by James Earl Jones he [Prowse] wasn’t privy to the secret, so instead, he was given alternate dialogue which is considerably less dramatic. But that in itself makes this a unique piece of history.’’

A percentage of proceeds from the auction will go to Alzheimer’s Research UK.