They are two of the most dedicated fan groups in sci-fi, so when both turned up to the same convention it was always going to get heated.
When Doctor Who fans gatecrashed the much-anticipated Norwich Star Wars Club open day, the family event quickly turned ugly.
Fans of the BBC1 series had turned up uninvited at the University of East Anglia convention last weekend.
But their 'long-running rivalry' meant police had to be called to keep the two warring sic-fi factions apart.
The event had returned after a three-year absence and reunited the four remaining actors who played bounty hunters in the George Lucas films.
The mood was soured at the Norwich Star Wars Club, however, when rival fans from the Norwich Sci-Fi Club were refused entry to the rival event.
Sci-fi Club treasurer Jim Poole then approached Doctor Who actor Graham Cole who was at the convention for an autograph.
But the event organiser Richard Walker, 63, confronted Mr Poole and demanded to know what the Sci-fi Club members were doing at the Star Wars club event.
Mr Walker claimed that the visiting club had been trying to undermine and embarrass the convention by posting negative comments on Facebook.
But Mr Poole said he had attended 'in good faith' to collect autographs from two actors for a Doctor Who signature diary to be auctioned for charity.
Both sides said there had been a long-running rivalry between the two groups and the events they organise.
Tensions were only diffused when police were called by worried sci-fi fanatics.
The secretary of the events organisers, Dominic Warner, yesterday (Wed) said: 'For four weeks leading up to the convention we have had nothing but nasty comments from that group.
'One of the group's committee members had been posting on social media that he was going to come and cause trouble.
'So when he turned up on Sunday afternoon we refused him entry into the convention.
'It all got a bit heated but it was our event and we were bang to rights not to let him in.
'Police were called and then I think a few of the people he was with were rounded up as well.
'The convention was still a rip roaring success though and we managed to fulfill our role which was putting smiles on people's faces.'
Norfolk Police said they had been called to reports of a man being assaulted at the get-together.
A police spokesman added: 'After lengthy investigation, talking to witnesses and reviewing good CCTV footage, it was confirmed that there was no assault.
'The two rival groups were spoken to and advised to keep out of each other's way.'