The creepiest moment in the 1981 BBC miniseries of Day of the Triffids has nothing to do with rubber monsters. Instead it involves a huge crowd of desperate blind people. Almost everybody in the world has gone blind thanks to some trippy lights, and our still-sighted hero gets caught in a huge crush of people trying to drag him out of his car. See an actual rubber monster clip, and find out the Triffids-Doctor Who connection, below the fold.
Actually, this latex monstrosity is genuinely scary, thanks to the total darkness and the use of little touches like the drop of oily/watery fluid dripping from its stinger. Triffids was produced by David Maloney, who directed most of the best Doctor Who episodes in the 1970s, and then went on to produce the first three seasons of Blake's 7. Many fans wish Maloney had taken over as Who producer instead of the self-indulgent John Nathan-Turner. If he had, it probably would have looked a lot like his Triffids.