The UK Open Textbook Project has released the UK Open Textbooks Report 2019.
Here's an excerpt:
The UK Open Textbooks project was conducted in several stages over the period of March 2017 to May 2019. The project tested two highly successful approaches to increasing engagement with, and use of, open textbooks. . . .
In the report we conclude that the awareness of OER and open textbooks is typically very low in the UK HE sector. However, awareness of open access publications is high, supported by the Finch Report and REF policy on open access deposition. Although existing knowledge of open textbooks was low, once educators were made aware of them, they expressed significant interest in their adoption. This provides an existing conceptual model and set of practices on which to build.