When you've written an award-winning fantasy series with a special pen it's not surprising you want to keep it forever.

But if you lose your favourite writing tool you might start thinking your next magnum opus may not be so successful.

That's the dilemma Oxford author Philip Pullman is facing, after carelessly mislaying his Montblanc.

The ballpoint pen made by a German manufacturer was kept in a green case and has, according to the author, gone missing.

He tweeted: "Lost: a green leather pen case, containing a Montblanc ballpoint pen and an ordinary pencil. I'm particularly attached to the pen, because I wrote His Dark Materials with it. If anyone finds it, I'd appreciate a tweet."

His fans are desperate to help but there is not much they can do at the moment as Mr Pullman has not indicated where he thinks he lost the precious package.

One Pullman follower, @InkyGuinjay tweeted back: "Oh gosh! I hope you find it...

"Also - remarkable of you that you handwrote the novel rather than use a typewriter or computer. My respect for you has increased."

It's perhaps not surprising that His Dark Materials is at the forefront of Mr Pullman's mind as the trilogy is being made into a star-studded series for the BBC, featuring actors including Logan star Dafne Keen as Lyra Belacqua and James McAvoy as polar explorer Lord Asriel.

The series is expected to air in 2019 and Logan star Dafne Keen has been cast as Lyra Belacqua, with James McAvoy cast in the role of polar explorer Lord Asriel.

Security was tight around Holywell Street in July when Cardiff-based Bad Wolf started filming scenes near the Bridge of Sighs.

Mr Pullman was feted by fans and the book trade when La Belle Sauvage was published in October last year.

It is the first instalment in a new trilogy, which the author has yet to complete.

Last month the author confessed he had been making too many commitments after almost collapsing at the Edinburgh book festival.

The Oxford Mail is keen to help with the search for the Montblanc but while the treasured pen remains missing it can offer the author an Oxford Mail biro as a temporary replacement:

Oxford Mail: