First shown: 19 December 1970 (US), 30 April 1971 (UK)
Director: Harry Booth
Writers: John Tully and Glyn Jones
Appearing apart from the Double Deckers:
Pat Coombs as Miss Fisher
Derek Royle as Mr. Beaumont
Jack Haig as the Short Workman
Bob Todd as the Big Workman
Lauri Lupino Lane as the Mayor
John Barrard as the Short Councillor
Reg Peters as the Tall Councillor
Note: I was on the road every weekend in May except the last, which I spent catching up with other things. Only two more episodes after this one, alas.
Plot
Local businessman Mr Beaumont wants to raze the Double Deckers' den and turn it into a car park. Two workmen are sent to clear it are frightened into retreat by the gang, who then sabotage Mr Beaumont's site visit with the Mayor and two councillors.

Glorious Moments
This episode is almost entirely slapstick, at the expense of Mr Beaumont...

...and also of the two workmen who are a delightful direct homage to Laurel and Hardy (their theme tune is referenced in the incidental music at one point).

Less glorious moments
There's not much here apart from the slapstick, and the kids don't actually get as much to do as the adult actors.
What's all this then?
The basic plot of the evil capitalist plan to destroy the place where the kids are having fun is most famously developed in Cliff Richard's The Young Ones (1961), also shot at Elstree. Melvyn Hayes, who appears in most Double Deckers episodes (but not this one) was of course in the next Cliff Richard film, Summer Holiday (1963).
Mr Beaumont, the evil authority figure, may have been intended to be a return appearance of Graham Stark's very similar character Mr Brimble from Episode 11, A Helping Hound - when he first appears, Billie says, "It's Mr Beaumont - he's come back!" although he has not previously appeared in the show.
Who's That?
John Tully, who gets part credit for the script, wrote three of the best-loved BBC TV adaptations of children's books in the 1970s - Tom's Midnight Garden (1974), Kizzy (1976) and The Phoenix and the Carpet (1976-77) - the last of these starred a young Gary Russell, who has gone on to other things. It's his only Double Deckers script, but given his track record I can't imagine that he was the writer of whom Glyn Jones complained that he had to rewrite the entire thing.
We have already seen Pat Coombs (Miss Fisher), who plays Doris in Episode 5, Happy Haunting, Jack Haig (the Short Workman), who plays Harvey the Toy Shop Assistant in Episode 2, The Case of the Missing Doughnut, and John Barrard (the Short Councillor) who plays the King of Diamonds in Episode 8, Scooper Strikes Out.
Derek Royle (Mr Beaumont), born in 1928, had a bit part in the Beatles' Magical Mystery Tour (1968), and ended his career in 'Allo 'Allo as Roger LeClerc (whose brother Ernest LeClerc was played by Jack Haig); the part was recast after his death in 1990. In the mid-1970s he and Pat Coombs appeared in a children's sit-com about a medical practice called Hogg's Back, in which he played the title character. He memorably also played Mr Leeman, the eponymous corpse in the classic Fawlty Towers episode The Kipper and the Corpse.

Bob Todd (the Tall Workman), born in 1921, had a long career as straight man to the likes of Benny Hill, Spike Milligan and Marty Feldman. He died in 1992.
Lauri Lupino Lane (the Mayor), also born in 1921, was the son of Lupino Lane, an Edwardian child actor who grew up to make the Lambeth Walk famous as the star of Me and My Girl (stage 1937, film 1939). Lauri has only ten credits on IMDB, the first being an appearance in his father's 1939 film and the last being another Mayor in Confessions of a Summer Camp Councillor (1977). He died in 1986. NB that IMDB incorrectly credits him as one of the councillors.
Reg Peters (the taller councillor) has nine minor IMDB credits between 1968 and 1971 followed by one in 1985, and that's it.
Where's that?
Entirely filmed in studio.
See you next week...
...for Up to Scratch.