I can't see classifying WITNESS as "low budget," not with the cast and director. It's a courtroom drama, and the court looks real. What strikes me about it is, unlike a lot of Hollywood-made "English" movies, including most of Hitchcock's US stuff set there (like DIAL M) and everything from WUTHERING HEIGHTS to THE BLACK SLEEP, I totally buy the illusion. Most of this is due to the casting, in my view.