T hese are heady days for fans of Sherlock Holmes. Arthur Conan Doyle's consulting detective may be a figure from Victorian fiction, but his appeal is as strong as ever with a new film, television series and book all in the offing.

The second BBC series of Sherlock begins on New Year's Day, while Guy Ritchie's second big screen adventure with the famous detective is out at cinemas now and doing brisk business.

Completing the Holmes hat-trick is Anthony Horowitz's The House Of Silk, the first Sherlock Holmes novel commissioned by the estate of Arthur Conan Doyle, which was published last month.

If anyone knows about all things Sherlock, it's Roger Johnson. A Chelmsford man born and bred, Roger is a long-standing member of The Sherlock Holmes Society of London and one of the world's leading experts on all matters regarding the great detective.

Being a prominent Sherlockian, Roger is always abreast of happenings in the world of Holmes and Watson, and has already seen the new television series and film, and got to interview Anthony Horowitz about the new novel at the British Library.

He approves of the latest Homes adventure in print, but with reservations.

"The book is very entertaining and is very dark," says Roger.

"The ultimate crime, the discovery at the end, is something that Conan Doyle would never have considered for a Sherlock Holmes story.

"It's a good read and I enjoyed it but I don't think it's the best post Conan Doyle Homes ever written."

Although Conan Doyle only wrote 56 short Holmes stories and four novels, there's now a burgeoning industry in Sherlock stories, the quality of which Roger says is highly variable.

"The quantity (of Holmes stories) is overwhelming. I don't try these days to keep up with it. There is a huge amount of drek out there which is as easily available as the good stuff, sometimes more so."

Roger and his wife Jean were invited on the set of the acclaimed BBC show Sherlock, when it was filming its second sereis in the summer, which proved to be an interesting experience.

"We were outside 221B Baker Street which isn't in Baker Street at all," says Roger.

"Mark Gatiss (series producer, writer, actor and huge Sherlock fan) explained it would be impossible to film in Baker Street. For one thing it's too busy. For another, you've got all these businesses using the name of Sherlock Holmes everywhere.

"We met with cast and crew which was very interesting indeed. We were able to watch the film as it was happening and on the monitor.

"We'd already met Benedict Cumberbatch (who plays Holmes), and Mark we'd known for a few years."

Roger says it was interesting to be on set because he knew Mark Gatiss had been thinking about a modern day Sherlock for a few years.

"In 2005, the guest of honour at the Sherlock Holmes Society's Annual Dinner was Stephen Fry, and possibly the best we've ever had and the only one I can remember getting a standing ovation. Steven brought as his guest, Mark Gatiss, and afterwards Mark said to our chairman "can I come back next year?"

"At the dinner in 2006, he brought Steven Moffatt and he told us of the idea that he and Stephen had for a series of Sherlock Holmes films set in the present day. They had worked all this out whilst travelling on the train between Cardiff and London for Doctor Who.

"We had an idea that these two guys knew what they were doing," says Roger. "We had an idea it would be in safe hands."

What does Roger make of the BBC series, which relocates Sherlock into modern day life with all its technological advances?

"I love it, I think it's brilliant. We were all curious as to how it would work and I know people who don't like it at all, but Steven and Mark have given us Holmes and Watson as they would be if Arthur Conan Doyle had been writing today.

"Benedict Cumberbatch has got the same sort of quality that Jeremy Brett brought to his early performances (in the 1980s Granada series) where you think 'this isn't Sherlock Holmes' but then you think 'hang on, yes it is, that is out of Conan Doyle."

Before the series returns, there's Guy Ritchie's second Sherlock Holmes film, A Game Of Shadows, which released earlier this month. Roger went to a preview screening, what does he think of this new adventure which pits Holmes against his nemesis, Professor Moriaty?

"The film is great fun, I enjoyed it immensely. It's better, I think, than the first film, the plot is better.

"There's a lot of slam-bam action in it as you'd expect from a Guy Ritchie film but it's very well done."

"Moriaty is played by Jared Harris, Richard Harris' son. I liked it, though he didn't give me quite the frisson the best Moriatys have done."

One of the great success of the Guy Ritchie films has been the crucial pairing of Robert Downey Jr and Jude Law as Holmes and Watson.

"They spark very well together," says Roger. "Robert Downey Jr acts spendidly, when he's on screen you know he's there.

"He's not really my Sherlock Holmes, for various reasons, mainly physical. He's shorter than his Watson, he's not rake thin, he doesn't have the beaky appearance but they work so well together, those two. And the relationship is crucial, it's what all the best Holmes and Watsons had."

So with Sherlock reinvented yet again for television and the big screen, why does Roger think this 19th century character has proved so enduring?

"I think it's partly because Sherlock Holmes is the iconic detective. Even attributes that don't originate from the stories, like the deerstalker hat – people see a deerstalker hat they think Sherlock Holmes, they think detective.

"There's also the fact the Sherlock Holmes stories are very unusual among Victorian literature, they're still read for pleasure, not because people have to read them, but people simply want to read them.

"They're just damn good stories."

Find out more about The Sherlock Holmes Society of London at www.sherlock-holmes.org.uk Sherlock Holmes: A Game of Shadows is at cinemas now. The series Sherlock returns to BBC1 on New Year's Day.