Having milked Dracula for all it was worth, in the early ’70s Hammer Films turned their gaze to other vampires and, taking advantage of the more relaxed censorship rules, created what is called the Karnstein Trilogy, very loosely based on Joseph Sheridan Le Fanu Carmilla (that you can find here as a free download in case you missed it).
The three movies in the cycle are The Vampire Lovers (1970), Lust for a Vampire (1971) and Twins of Evil (1971), and are considered classics – and I will have to write about them sooner or later.
The Karnstein vampires are different from their Transylvanian counterparts, being generally female, much more inclined to nudity and most importantly being able to go about in open daylight.
The Karnstein vampires would make two more appearances in the Hammer Films catalog: once in Captain Kronos, Vampire Hunter, in 1974 and before that, a band of Karnstein vampires in all but name brought madness and death to a small Serbian Village in Vampire Circus (1972).

Directed by Robert Young and produced by Michael Carreras, Vampire Circus is not the most popular Hammer movie, and it seems to have faded into obscurity. Which is a pity, because while it was shot in record time (six weeks) and under the usual Hammer financial constraints, it’s fun, and refreshingly original.

The plot in a nutshell, courtesy of IMDB: A village in Nineteenth Century Europe is at first relieved when a circus breaks through the quarantine to take the local’s minds off the plague. But their troubles are only beginning as children begin to disappear and the legacy of a long-ago massacre is brought to light.

The movie recycles part of the sets of Twins of Evil (another connection with the Karnstein films), and especially the scenes set in the circus may appear strangely stage-y. Robert Young manages however to turn these scenes in something akin to dream sequences – the circus is the place of the imagination, and it is within the imagination that the vampires hide and wait for their revenge. The villagers, trapped not only in the quarantine zone, but most importantly in their small-town mindset, have little hopes of facing the menace.

Vampire Circus features fiery-headed Adrienne Corri as the ultimate incarnation of the gypsy queen and circus ring-mistress, and also Lalla Ward, future companion of Doctor Who (and wife of evolutionary biologist Richard Dawkins), as an acrobat and vampiress. David Prowse, that would a few years later fill the black costume of Darth Vader, appears as a circus strongman. The rest of the cast is composed of oft-seen British character actors and assorted unknowns – which actually enhances the overall effect, as we do not know who’s going to face a premature end as the story evolves. An actual British circus provided extra artists and a few numbers to spice up the circus scenes.

What the movie lacks in terms of sets, special effects and plot, is more than compensated by the grotesque and macabre elements that are liberally sprinkled through the 87 minutes of the film. Vampire Circus comes dangerously close to being art-house in some of its directorial choices, but in this – and in the more restrained sexyness when compared to the Karnstein movies – is its strength. It does not horrify, but it intrigues, and it plays as a mystery at times.

I had caught this in some third-rate movie theatre as a kid, and I have re-watched it recently, and must rank it as one of my favorite Hammer movies.
It may be a guilty pleasure, but the pleasure far outweighs the guilt.