Refreshing my memory about this one, I came across a very fine analysis from an IMDB review named "the red duchess", which I think amplifies what Mark is referencing. (I'm bookmarking that reviewer to explore more of her/his writings based on this sample...)

With its obtrusive framing, its heightened, unrealistic colour, its blatantly artificial sets, and its stylised acting, the film seems more like a 50s melodrama by Sirk, or a mid-period thriller by Chabrol, than a British costume drama. Even the beautiful English countryside, so skilfully evoked as to be almost tactile, seems fake, a gorgeous series of painted props.

This clash between narrative immediacy and formal alienation allows Losey to create a startlingly modernist work. As Fassbinder remarked of Sirk, it is the villains who are the sympathetic characters here, not the pallid heroes. For instance, the heroine is imprisoned so Belle and her gypsy lover can make a fortune, but it is Belle who is given the film's most miraculous shot, a composition of the vast rural landscape that pulls back to be revealed framed through a barred window, with Belle looking out, imprisoned when she seems at her most narratively powerful.

Typically, Losey is not interested in romantic stereotypes, but in the economic circumstances that turn people into what they are - it is money that determines characters' actions, even the 'good' ones, and drives the plot - in one Hitchcockian shot, the camera obliterates the human players and closes in on a purse of coins.

More importantly, the film is a first attempt at 'The Servant', the story of an aristocrat brought low by deceptive interlopers, potentially sterile economic arguments are shown to have their roots in sexual neurosis and attendant issues of power, social and sexual, and the body and gender. The way the despised outcasts bring ruin to the decadent gentry by increasingly barbarous schemes is filmed with barely concealed glee by Losey, even as Belle becomes an oppressor and thence self-destructive (Belle becomes tainted by power, Jed remains true to himself - a gendered 'political' argument?) - you imagine the director's heart is with the vandal who, like Losey the American in Britain, sneaks into the mansion at night, and starts smashing and shredding the decor.