By Ian Youngs BBC News Online entertainment staff

Douglas Adams died after a heart attack in 2001

Adams' mother, sisters, brother and daughter all feature as extras, according to the executive producer.

"They are extras in the scene when earth learns of its impending destruction," Robbie Stamp said.

Filming has been under way on the movie for more than three months. Adams died after a heart attack in 2001.

Mr Stamp wrote on the film's website he felt "pride that we have come this far and real sadness that Douglas is not here to share it".

"But we have been able to film some scenes which included Douglas' family."

The Office star Martin Freeman is to play Arthur Dent in the film

Adams' half-brother James Thrift told the author's official site that being on set "makes you realise how he not only created something so intrinsically valuable to the world at large, but also how much he inspired those around him so much".

"That inspiration now seems to be firmly with the film production crew," he wrote.

The scene was filmed in the City of London in July and forms an early part of the story where human Arthur Dent and his mysterious friend Ford Prefect beam up to a passing alien spacecraft, which goes on to destroy Earth.

Dent, played by The Office star Martin Freeman, and Prefect, played by rapper Mos Def, proceed to have comic adventures around the galaxy with a cast of strange beings.

Adams' official site said of the filming: "The production team were determined that everything had to be perfect and packed with detail - from familiar faces rushing for the not-so-safety of the Underground station, to posters in tea-shop windows and street signs.

The Hitchhiker's Guide became a TV series in 1981

"We're not going to spoil any surprises, but when we weren't running around in blind terror we couldn't help but notice enough in-jokes and clever references to keep the DVD bonus feature film crew busy all day."

Adams' original 1977 radio scripts were fashioned into a book and then a TV series in the early 1980s.

A feature film has been in the pipeline ever since - described by Adams as "20 years of constipation".

But it finally got off the ground after the author's death, led by Mr Stamp, Adams' friend and business partner.