Insurance is provided for all u3as by the u3a National body – “The Third Age Trust”. A questions and answers document explaining the details can be found here:
u3a Insurance – Frequently Asked Questions
Please note, this document was downloaded from the National u3a site on 9.9.22 and although frequent changes are unlikely, you are advised to visit their site https://www.u3a.org.uk/index.php, to obtain the latest version. (You will need to create an account and log in to obtain information from the u3a website, but there is a lot available, covering a wide range of topics. A search for “Insurance” found this document)