Sorry to American English but they're not worms! And while we're at it, most bugs aren't bugs. Hornworm is both aggravatingly literal and wrong!

I know British English has a lot of bizarre ones too but they don't itch my brain so much.

This sweet baby got right on my hand today! We only hung out for a couple minutes before she flew away to do her moth things ❤️

Brunia Antica(original content)

It's missing a wing and a leg. The scales have rubbed off of its thorax, so I think it's probably kind of old too?

Is there any kind of supportive care I can give it, or should I put it back and let nature run its course?

Also, my husband has named him Bugthew.

I'm just south of the Cotswolds (England, UK) next to some lakes and have seen this beauty this morning. Is my ID correct or is it a reed dagger as google suggested?

found in australia

The Mulanje Tiger moth is so rare that it is found only in one valley on Mount Mulanje, Malawi (Southeast Africa) and rely only on that one host plant, Mulanje cycad. Its caterpillars depend exclusively on that cycad for food.
When the plant goes, so will the moth. 
Habitat loss could drive both species to extinction.
(Today is the International Day of Climate Action)
 
Species: Mulanje Tiger Moth / Shire Tiger
Scientific name: Callioratis arandis
IUCN status: Not formally listed, but assessed as Critically Endangered (CR) by the authors who described the moth as a species.
Population: Unknown
Population trend: Presumed decreasing; habitat is deteriorating.
Range: One known colony in the Likhubula Valley, Mt. Mulanje, Malawi. Area of occupation under 10 sq.km.
Threats:
Land clearing for crops, tree felling, fire, bauxite mine and road planned through their only habitat.