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The man who wrote Monday night's dramatic Coronation Street episode says he did not see it until he watched it with his family when it was broadcast.

The soap featured an explosion and a tram crash and was watched by an average 13m viewers.

Joe Turner, who lives in Abergavenny, Monmouthshire, said no advance copies were given to the writing team because producers wanted to keep it under wraps.

"I was in the odd position of not having seen it before," said Mr Turner.

"Normally we get DVDs in advance but because they were trying to keep as much secrecy as possible about it, I actually had the thrill of sitting with my family last night with a very nice bottle of wine and enjoying it as it went out!"

The action-packed storyline was part of celebrations for Coronation Street's 50th anniversary.

An explosion damaged the viaduct causing a tram to crash onto houses in the street, leaving the fate of many characters uncertain.

Mr Turner said the storyline had been under development for some time.

"We've been planning the 50th anniversary for about a year and some of us on the writing team were more keen to actually do it low key, and to have very quiet kind of stories, and maybe just Ken doing a little speech in the pub or something like that," he told 91�ȱ� Radfio Wales.

"But our producer, bless him, persuaded us that what we should do, and what we have done, and what we will see from now on, is that we have actually taken three very big stories and built them to a series of climaxes.

"Then we have dropped a tram and a massive explosion on the street."

Mr Turner said there were 17 or 18 writers on the team, half a dozen "storyliners", a story editor, a producer and an assistant producer.

"We have a meeting every three weeks and we spend two or three days in Manchester," he said.

"We just do what normal people do and we just sit around going 'what do you think happens next? What do you think is going to happen with Kevin and Sally? Do you think Tyrone is going to leave Molly? What do you think we should do next?

"It's a fabulous job. I sit here in my little office in Abergavenny making up stories and writing episodes, and then two or three months later they spend a million quid on organising that stunt that they did last night!"

He said the episode was "pretty close" to how he had originally envisaged it.

"The thing that's exciting about Coronation Street, because we have to make so many episodes, we have to get it right first time so we put a lot of effort into the preparation of these things," he said.

"Early on when I was writing that episode, we had special effects people do a kind of cartoon version of it and we watched it at one of our conferences.

"It was like a little sort of manga version of cartoon Kevin Websters and characters, and how the tram would come off the viaduct and from what angles we would see it."

Monday night's episodes netted an average 13m viewers, overnight figures show.

The anniversary of the broadcast of the first episode will be marked on Thursday with a live, hour-long instalment.