Hi Andy, it works in the validator, but we don’t see images on the timeline if the following link is used to share the page:
<a class="share-twitter" href="JavaScript:newPopup('http://www.twitter.com/share?url=https://raceforlife.cancerresearchuk.org/choose-your-event/events/london-blackheath-5k-2016-07-03-1130.html&text=Enter your local Race for Life 5k today and help us show cancer that hell hath no fury like a woman in pink.');"></a>
Does this link not pick up the twitter card?