Can anyone please help identify this insect. It seems to be some sort of caterpillar but I'm stumped.
- Location is in Suffolk, United Kingdom
- Length is around 1cm, width is perhaps 4 or 5mm.
Image opens a video clip on YouTube.
That appears to a "bag worm", which is as you surmised a caterpillar.
This suggest that it is from the family Psychidae, but I won't even try to guess at the species. However, if you see any adults you may be able to identify them using this website.
An example image of an North American species: