'Sherlock' seasons 4 and 5 are already planned out

LONDON, Jan. 9 (UPI) -- Steven Moffat says he and his "Sherlock" co-creator Mark Gatiss have already planned out seasons 4 and 5 of the British mystery series.

"Rather excitingly, Mark and I, for no particular reason, we just got out of the rain and sat at the top of the ['Sherlock'] production bus ... and we just started plotting out what we could do in the future," the Radio Times reported Moffat said at a British Academy of Film and Television event this week.

"And we plotted out the whole of series 4 and 5," he said. "The ideas we had that day, I thought were the best we've ever had."

Starring Benedict Cumberbatch and Martin Freeman, the contemporary London-set show recently began airing its third season in the United Kingdom. Season 3 of the show will premiere in the United States Jan. 19 on PBS.

Although future seasons of "Sherlock" have not officially been ordered, Cumberbatch and Freeman have publicly expressed their interest in staying on the series, E! News said.