Definitely a classic. WAM on the mainsteam cinema screen before it became generally known as a fetish. (IIRC, she "suffered" water, beans and finally chocolate )
Ann Margaret took part in several films in which she got into a mess, one wonders if she liked it? Of course in Tommy she also went in to the sea fully clothed too. My first reaction, as we were struggling to buy furniture at the time was what a waste of a white leather settee. I rather liked the scene too of course. Ken Russell was always over the top in directing his films, should you seek them out you may not be disappointed. He also directed a film in which the very first mainstream depiction of two naked males wrestled before a large fireplace which had an equally large roaring fire. Always going just that bit (too much?) further than his contemporaries.
I always thought that it would have been destroyed, but the outfit was sold at auction a couple of years ago for nearly $11,000! Details here in the sale catalogue (which I think was posted here at the time).
See letter of provenance attached and below (with some nice pictures!)