This https://en.wikipedia.org/wiki/HTTP/2#Encryption says
HTTP/2 is defined for both HTTP URIs (i.e. without encryption) and for HTTPS URIs (over TLS, where TLS 1.2 or newer is required).[25]
but testing on Google I get different results:
curl --http2 -I http://www.google.co.uk
HTTP/1.1 200 OK
curl --http2 -I https://www.google.co.uk
HTTP/2 200
The same goes for other domains. Any explanation?