Watch out! The aliens are coming (again)

But when you spot a shorter-than-expected Darth Vader strolling down Coppergate, as one colleague did recently, you know something is afoot...

And so it is. This weekend, York will be subjected to a full-on alien invasion. And not just aliens. Alongside imperial stormtroopers, Alien queens, Jabba the Hutts, Transformers and at least one time-travelling Time Lord there will be zombies, superheroes, a (miniature) Direwolf from TV's Game of Thrones...and several Harry Potter-style message-carrying owls.

Yes, York's annual Unleashed festival, a Comic Con-style science fiction and fantasy convention, is returning to York for a third run.

Assorted aliens in Stonegate prepare for the 2017 York Unleashed event Picture: Lee Hall

And this time it will be bigger and better than ever, says organiser Lee Hall, of Middlesbrough-based Unleashed Events.

Unleashed stage several such events each year - but the York one is undoubtedly the biggest, Lee says. The first event, in 2015, attracted just under 2,000 visitors. Last year it was almost 4,000. "And judging by pre-sales, we're expecting more than 5,000 this year," he says.

That Darth Vader spotted by a colleague in Coppergate actually was one of his, Lee admits, sent to York on a mission to promote this Sunday's event at Knavesmire. But short? He was no such thing. "Your colleague must have been further away from him than he thought he was!"

In the way of these things, many of those who head for the Knavesmire on Sunday will be dressed up for the occasion. Thousands of assorted aliens, monsters, superheroes and zombies descending on the racecourse all sounds a bit much.

Giulietta Zawadzki as the alien queen at last year's York Unleashed

But these won't all be Cosplayers - hard-core sci-fi fans who spend a fortune on getting the best, most realistic costume they can afford. Many of them will be ordinary families and children just up for a great day out, who've put together a simple fancy dress costume, Lee says.

What will unite them is a love of the sci-fi, horror, and the weird and the wonderful generally.

There was a time when loving sci fi was seen as geeky and uncool, Lee admits.

But with Marvel films and Star Wars dominating Hollywood and pulling huge audiences, those days have long gone. "It is mainstream now," Lee says.

Hence this weekend's alien invasion of the ancient city of York.

A Jawa from the Star Wars films at the 2015 event

Alongside the walking, talking monsters, there will be a fair few familiar (and fairly familiar) faces from film and TV who have played aliens onscreen - among them Peter Davison, the fifth Doctor Who; and Julian Glover, who played the odious Grand Maester Pycelle on Game of Thrones (see panel).

York, of course, is known more for its Romans and Vikings, ghosts and criminals from years past than for its visitors from outer space.

So what do the city's more traditional residents make of this alien invasion?

Sigwulf - aka Neil Tattersall of Northern Forge's 'Original Viking Walk of York' - has got nothing against visitors from far away.

After all, Vikings themselves were both travellers and invaders, he points out. "They roved as far as Byzantium - Istanbul - so they would have had no problem with someone from a galaxy far, far away," he says.

And if things were somehow to turn a little edgy, how does he think a Viking would get on in a hand-to-hand fight with Darth Vader?

Just make it a fair fight: Sigwulf (aka Neil Tattersall)

It wouldn't be a fair contest, Sigwulf protests. "You'd have to back the one with the light sabre." If the fight was evened up a bit and that light sabre was somehow taken out of the equation, however, then it would be a different matter. "Then I think the Viking would do OK."

Fortunately it won't come to that. Sigwulf - or, at least, Neil - has been booked by English Heritage on Sunday to take part in an event at Rievaulx. Which should be just about far enough away, even in Luke Skywalker's Landspeeder...

York's foremost poisoner, Mad Alice, won't be there, either. Alice is reputed to have been hanged at York Castle in the 1820s for poisoning her husband. Her ghost, played by actress Alicia Stabler, still gives regular Mad Alice tours of York, in which she introduces visitors to the city's bloody and unsavoury past.

Mad Alice: welcomes an alien invasion

So what does she think of aliens on Knavesmire?

"I was hoping to go!" she says. "Unfortunately I'll be working that day. But I think it's an absolutely great event, and a good way to get different people coming to York."

York's own alien invasion, as recommended by Mad Alice. Sounds like one not to be missed...

• York Unleashed, 10am-5pm, Sunday August 13, York Racecourse. Entry £6 on the door (under 12s £4, under 5s free). Children and families very welcome.

Festival highlights

There will be many highlights to be enjoyed by visitors to York Unleashed, including a Ghostbusters stage show, seven eight-foot-tall Transformers, a Zombie Survival School, a Lightsabre Training Academy, a Harry Potter owl display and, of course, superheroes.

These will include Iron Man, Batman, Thor, the Hulk, Deadpool and 'lots of Spidermen', according to organiser Lee Hall. There will also, for good measure, be a life-sized dinosaur wandering about; some Transformers; and a miniature Direwolf (which sounds pretty much like an ordinary-sized dog, but there you go).

The Yorkshire Ghostbusters arrive at the 2015 event at York Racecourse

There will be stalls, of course, selling comics, graphic novels, costumes, books, t-shirts, art, jewellery and much more. But perhaps the biggest attraction of all will be the chance to meet some of the stars (big and small) of film and TV who have appeared in sci-fi and fantasy film and shows.

The provisional line-up includes Peter Davison (the fifth Doctor Who) and his companion Nyssa (Sarah Sutton); Julian Glover, who played Grand Maester Pycelle in Game of Thrones; Mel Pickup (Athgar Heece in Star Wars: Episode VII); Spencer Wilding (who has played both Darth Vader and a white walker from GoT) and Pam Rose (an alien woman, Leesub Sirln, hanging out in Chalmun's Cantina in Star Wars: Episode IV).

These will all be hanging out in a first floor bar at the racecourse. You be able to buy photographs which you can ask the stars to autograph, says Lee - but you won't need to fork out for a photo if you don't want to. "You can just go up for a chat."

A chat with the Fifth Doctor? Sounds like a good way to spend a Sunday afternoon. Just don't mention Siegfried Farnon...