The Day of the Triffids - watch online: streaming, buy or rent
Currently you are able to watch "The Day of the Triffids" streaming on Cultpix or for free with ads on Pluto TV. It is also possible to rent "The Day of the Triffids" on Amazon Video online and to download it on Amazon Video.
You can also stream the title for free on JustWatchTV, Plex.