SHERLOCK is all but over, its viewing figures said to be in “freefall” given that it had picked up an audience of only 5.9 million, even fewer than the Antiques Roadshow or Countryfile.

But what lessons have been learned from the demise of this once great BBC idea which became an international success story? Let’s hope several.

The most obvious is that you can’t treat viewers as though they have the intelligence of a deerstalker. You can’t cheat them by explaining an immensely complicated plot away by saying it was all a dream. That device went out of the window when Dorothy woke up in bed in Kansas clutching Toto.

We can’t have daft stories in which an otherwise healthy boy has a fatal seizure while dressed as a car seat. You can’t have Sherlock become a Ninja warrior when he’s only ever been trained in sneering and only ever fought a bad cold. And you can’t have Mrs Hudson go from making the tea and serving up homilies to driving an Aston Martin in less than three seconds.

The second lesson is that BBC bosses must read the story of the emperor’s new clothes. If they do they will stop reading the old crits of the series, which began with a bang when Benedict Cumberbatch brought exactly the right note to the character who could tell what a person had for breakfast back in January 1, 1970 thanks to the stain on his tie and the fact that Carole King was playing on their Ipod when they were killed.

We loved the wedding episode. We loved the one featuring the woman who wandered the house wearing nothing but her Louboutins.

But then it all got sillier and sillier because no one had the nerve or power to say to writers Steven Moffat (a very talented man) and Mark Gatiss (who plays Sherlocks’s brother Mycroft), “Look lads, I think you’ve lost the plot here”.

And that brings us to another problem. Once upon a time, writers wrote scripts and a producer got them to take out the silly bits. These days, BBC compliance sees writers jump through several hoops to get a show on the air. Paradoxically, Sherlock’s writer Steven Moffat doesn’t seem to be told when he’s murdering a storyline.

Could this be anything to do with the fact he’s married to the producer and one of the executive producers is his mother-in-law?

Is a producer able to say to their partner: “Fancy a cosy night in on Saturday with a bottle of wine?” And then in the next breath say: “By the way, there is no way on earth the bad guy could have followed Sherlock around the globe without being spotted, given that Sherlock is the cleverest detective in all the universe.”

It’s easy to understand why the Sherlock team were given a lot of leeway. After all, it did help BBC Worldwide pull in an incredible £175 million a year, licensed to some 224 territories.

But don’t ask the viewer to fill in plot holes. This isn’t like asking the council to fill in pot holes. The viewers are there to be entertained, not to have to try and interpret a writer’s whimsy. And let’s stop the same nonsense on Dr Who before it becomes lost up its own time continuum.