Image caption The last special edition was 1999's Blackadder: Back and Forth

A draft script for a Christmas episode of Blackadder has come to light during research for a new book about the BBC's classic comedy series.

Blackadder in Bethlehem sees Rowan Atkinson's character as the owner of the inn where Joseph and Mary seek a bed for the night.

The story also features Baldrick, the Three Kings - and a talking turkey.

Written in 1988, the script was given to comedy historian Jem Roberts by writer Richard Curtis.

Roberts describes it as "completely unofficial Blackadder".

Fragments of the unfinished script appear in his book, The History of the Black Adder, which is published later this week.

In the book, Curtis says that he abandoned the idea "for fear it would cause too much offence".

Instead, it was the Dickensian-themed Blackadder's Christmas Carol that went into production, and was broadcast on 23 December 1988.

Blackadder ran for four series between 1983 and 1989, starring Atkinson as Blackadder and Tony Robinson as his dogsbody Baldrick.

There were also some stand-alone stories, the last of which was Blackadder: Back and Forth in 1999.

"When you write a book about a comedy world, there is a dream that you'll be invited into this Ali Baba's cave of unbelievable archive material," Roberts told the BBC. "I always presumed that would never be the case with Blackadder."

But Roberts was amazed when he was handed the previously unseen script while interviewing Curtis at his offices in Notting Hill.

"He printed out a document from his computer and said, 'see what you want to do with this'.

"My jaw dropped when I saw I was holding a lost Blackadder script.

Roberts added: "He wrote on the script that one of the reasons it didn't get used was because it was a strange cross between Fawlty Towers and Life of Brian.

"He didn't think he was going to make it compare to either of them. That's his reason for it never getting any further than it did."

Image caption Author Jem Roberts said the book was intended as the work of a "devoted fan"

Set on 24 December at the Blackadder Inn in Bethlehem, the opening scene features an exchange in the foyer between Blackadder and Baldrick about getting a turkey for the "most important night in the history of this hotel".

In the next scene, Baldrick is in the kitchen with a turkey which starts to remonstrate with him about being plucked and eaten.

Later, Joseph arrives looking for a room. Blackadder offers him Baldrick's lodgings.

BLACKADDER: How about I offer you this young man's room?

JOSEPH: That sounds excellent.

BLACKADDER: Yes. It's not that excellent - less of a room, more of a manger.

"It wasn't a huge script, there were massive amounts missing," explains Roberts. "It's the rough workings of a comic genius."

The author said he wanted to write the history of Blackadder from the point of view of a "devoted fan", to mark the 30th anniversary of the first pilot episode of The Black Adder.

The book was written with the co-operation of writers Richard Curtis and Ben Elton, producer John Lloyd and the cast and crew.

Roberts's previous book was The Fully Authorised History of 'I'm Sorry I Haven't a Clue'.

But what did Roberts think of the talking turkey scene in Curtis's re-discovered script?

"In the Blackadder universe there are ghosts and witches, so there could have been talking turkeys - why not?"

"If they had made Blackadder in Bethlehem, it would have been very off-the-wall."