As above. I’ve looked at a few but nothing seems particularly highly recommended. The Ortlieb system seems to be a bit off a faff to attach the backpack ‘carrier’ and some of the others look as though the clips might dig into to your back. Looking for something around 18l. Not particularly excited if it doesn’t exist but didn’t want to miss anything obvious before giving in

Rik, Arkel make one, its pricy though.

http://www.arkel-od.com/en/pannier-backpack.html

Yep. The bug is looking like a winner at the moment but it is indeed pricey. A better option might just be a humungous pannier and sling a regular backpack into it

This US article might be useful

http://www.cyclingabout.com/list-of-convertible-backpack-panniers-that-can-be-strapped-to-your-back-or-bike/

Thanks, its a good list but not much review really. Some of them look great like the Blackburn but are impractical in use as for the Blackburn you attach is to your rack with velcro straps which is a hassle as well as a little scary