YA novel set in London featuring a teenage Sherlock wannabe

Question

I'm looking for a novel I owned and read in the 1980s.  Here's the little I can remember about it:

The main character is a teenage boy who has studied the Sherlock Holmes books and tries to follow the great detective's methods.  (For example, I think he described one puzzle as a “three-gobstopper problem”.)

It's written in English and set in London, probably a suburb, and is contemporary and low-key.  He and his friends have a large room/clubhouse on the upper floor of a warehouse or similar building.  They get on the trail of some baddies who have a (blue?) van, and a hut or other hideout somewhere in the Essex marshes; the MC later identifies splashes of Essex mud on the van from the colour.  (I don't remember what the baddies had done, but it might have involved a kidnapping.)  Near the end, he and his friends get holed up in their clubhouse, watching the sun go down, knowing that the baddies are out there, closing in, and will attack once it gets dark…

This was a UK paperback, maybe a Puffin, probably fairly small, and I think it had a plain light-blue cover with a simple monochrome print or line drawing on the front (unless I'm confusing it with the Puffin edition of The Hound Of The Baskervilles).  [EDIT: A Piccolo; and yes, I was getting the cover confused: it's mostly black-on-white]

It didn't seem like part of a series.  [EDIT: Actually the first in a series, though not billed as such.]  I think it was fairly new at the time, so probably published in the 1970s or early-to-mid 1980s.  [EDIT: 1980]  I may have bought it new from a book club/catalogue such as the Puffin Club (though I've checked all I could find online, and nothing rings a bell).

That's all I can remember, I'm afraid — except that it appealed to teenage me!

Answer 1

Is it possible that you're referring to a book in the Baker Street Irregulars series by Terrance Dicks? It features a group of kids in London who emulate Sherlock Holmes and his methods. You can borrow a copy of the first book, The Case of the Missing Masterpiece here, and indeed, there is a blue Essex van with mud on it driven by the criminals.

Page 109

Dan's jeans were torn and he had a nasty-looking cut on his knee, but otherwise he was unhurt. A workman on a bike stopped at the curb. "You all right, son? I tried to get the number for you, but there was mud all over the plates. It was a blue Volkswagen van, though, I can tell you that."

Page 128

" ... There was Essex mud on the van. And where would you send a nervous friend who needed a bit of peace and quiet?"

And it's apparently a "three-sour-ball problem".

He pushed aside his dossier and slumped into his old armchair. Definitely what Sherlock Holmes would have called a three-pipe problem. But Dan didn't smoke, and a three-sour-ball problem didn't have the same ring to it. Still, there was something else Holmes used to do to help him think. Dan lugged his violin case from under his bed and took out the violin. He began scraping away, trying to produce those ''sonorous and melancholy chords" with which Sherlock Holmes used to madden Doctor Watson.

FWIW, I found it on the TV Tropes page for Kid Detective.