Need help from movie experts

Hi everyone,

I would appreciate some help working out the title of a British movie I saw way back (I think around 1968) - unfortunately I don't recall any part of the title or the names of any of the actors in it.

All I can remember is that there was a guy who drove a classic american car like a big chevy or something out to a farmhouse and killed the family there.

There's a shot beforehand when he first arrives that shows a lawn mower puttering away on the grass by itself then shows the gardener who's been murdered.

Also the killer wore cowboy boots with a star on them which was the hint that gave away his identity - he also whistled eerily when he walked around before murdering or knocking on doors.

I hope this rings a bell for someone - thanks for your help in advance!!

It's 1971's "Blind Terror," which was known as "See No Evil" in the U.S. with Mia Farrow as the blind heroine, stalked by the killer. Unless there are two films out there where the killer wears cowboy boots with a star on them.