Steven Moffat, the Paisley-born executive producer and co-creator of Sherlock, said he was at a loss to explain its success as the show's third series ended with an average audience of 8.8 million watching the season's climax.
Mr Moffat said: "It isn't supposed to be like this. Sherlock began life as a surprise hit, and now in its third series, it's rating higher than ever.
"This show, which we all thought would be our vanity project destined for three million in the ratings and possibly an award from an obscure European festival, has become a barnstorming international phenomenon."
Moffat, who wrote the series with Mark Gatiss, went on: "If I live to be a very old man, I might be able to explain how any of that happened - drop me a line in about 40 years, I'll do my best."