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Coronation Street producers are taking unprecedented steps to keep their 50th anniversary storylines under wraps as filming is due to begin.

It is known that a tram will crash onto the street, killing some characters and destroying buildings. But ITV is keen to stop further details leaking out.

"We're actually being given scripts with just our own parts in it," said William Roache, who plays Ken Barlow.

"We don't read the other people's parts. I've never known such secrecy."

A street party has been held on the set in Manchester, where the cast is due to start shooting the first anniversary storylines on Monday.

Roache, who has been in the show since the first episode, has been named by Guinness World Records as the world's longest-serving soap actor.

Asked whether Ken might be written out, Roache told ´óÏó´«Ã½ News: "There's a great mystery around what's happening at the 50th anniversary.

"They're really keeping it close to their chests. So we don't know. Some of us might make shrewd guesses but I'm not going to talk about those."

Keith Duffy, who plays Ciaran McCarthy, said: "Everything is pretty much behind closed doors at the minute. Even the actors themselves don't really know what's happening.

"I know this viaduct is coming down with a tram, I just hope I'm not underneath it."

While actors are usually given scripts a week in advance, they may only find out about the crucial scenes a day or two before filming, Duffy said.

"They want to keep it tight-lipped. Every good storyline in any good soap always gets leaks and they're just trying their best this time around to try and keep it schtum."

Producer Phil Collinson promised that the anniversary episodes would entail "tragedy and destruction on a previously unseen scale".

"The scripts are written, they're all locked away upstairs in a big cupboard," he said. "Literally under lock and key. We know where the story's going and we start filming on Monday."

Mr Collinson has enlisted special effects company The Mill, which won an Oscar for Gladiator and has worked on Doctor Who.

"They will be the biggest, most spectacular episodes ever filmed," Mr Collinson said. "The Mill are very used to creating memorable, spectacular, effects-driven television."

The show will also feature a live episode, which will portray the aftermath of the tram crash.

As well as creating the explosive scenes, special effects will be used to show the rest of the fictional Manchester borough of Weatherfield for the first time, Mr Collinson revealed.

"The special effects work we'll do isn't just about crashing the tram," he explained. "We're going to see Coronation Street in the context of the wider world.

"So we're going to have great big wide shots that show you the rest of Weatherfield. Life has begun and ended at the top and bottom of the street, but for the first time we're going to see the wider world."

Jack Duckworth, played by Bill Tarmey, is one character who will leave before the end of the year. His final scenes - which are not part of the tram crash - will feature the return of his on-screen wife Vera, who died in 2008.

Mr Collinson declined to give details about the nature of her appearance, but did say: "She's not a ghost, she doesn't come in on a wire. It's beautiful and poignant."