DePatie-Freleng Enterprises did several theatrical cartoons series featuring the likes of Pink Panther, Ant and the Aardvark and The Inspector and others throughout the 60s and 70s. Of which The Inspector series is to me one of their better ones, perhaps second after Pink Panther, evident from that it is one of their better known and longer running ones. May not love all the Inspector cartoons, but do like most of the series more than most cartoons in some of the other theatrical series.
'London Derriere' is the twenty fourth The Inspector cartoon, of thirty four, and to me it is among the cartoons in the series somewhere in the middle which is not a bad position actually. It is well done in most areas, is amusing enough and The Inspector never stopped being a compelling character and is still very much one here. Albeit it doesn't make me go wow or bust a gut from laughing, much of 'London Derriere' is done very well but nothing as such is exceptional.
Although The Inspector cartoons are not really known or to be seen for their originality, even with a different setting the story is very formulaic and quite high on the predictability factor. It does take a little too long to get going and occasionally the timing could have been sharper.
More variety in the gags would have helped too, do agree that it is one-joke and although it didn't feel too stretched and wasn't unfunny it did get on the repetitive side at times. While the jewel thief character Louie Le Swipe is decent conflict and contrasts well with The Inspector, he is pretty forgettable and slightly derivative of other adversaries in the series.
The cartoon does manage to work though, and that The Inspector is a character that is both funny and compelling, as well as endearing despite all the bumbling (which thankfully isn't too overdone), plays a major part in this. 'London Derriere' does have a good deal of energy and both the endearingly clumsy and amusing physical comedy and ironic verbal humour come over well. Do agree that the ending is the best part. Did like the Scotland Yard character and the personalities for both characters contrast well, the chemistry gels too.
Voice acting is typically strong, still have no issues with Pat Harrington Jr. The animation is simple but colourful and charming in its simplicity. The music never felt too brash or worked against the action, matching the cartoon's tone well.
In conclusion, decent if unexceptional. 6/10