In reply to Calum Childs.

You may have come across an AMP-powered site before but just didn't realize it. For example, these sites are native AMP:

https://www.bmw.com/
https://tasty.co/
https://www.iene.mediaset.it/
https://winefolly.com/
https://medinathoughts.com/
https://xwp.co/
https://www.ampproject.org/

Note also that Twitter and Bing also serve links to AMP pages when available on mobile. So Google is not the only way you can encounter an AMP page.