I have slowed the cron job down to 10 minutes until this has been got to the bottom of.

I think something is in the mail queue that is blowing up the cron_bridge.php

User posted ~30MB of images, across lots of images, which is using a lot of memory to convert to a MIME email. Thinking of how to workaround now...

5MB image embedding limit is now applied across all files, rather than per-file.

Thanks Chris.
Out of interest who was the user ?

http://vwgolfmk1.org.uk/forum/index.php?page=topicview&id=show-meet-pictures-and_2%2Fultimate-dubs-2014_2#post_1391418