In reply to afx22: We've got one of The North Face Messenger bags mentioned above.
We don't us it too much (generally work stuff or as a travel or carry-on bag) but it's a good, robust and attractive bit of kit, albeit rather overpriced if you pay full retail price.
I've got a DMM Flight that I use for all my indoor, sport climbing and single pitch cragging which is superb but way too big for your needs. Ideally someone needs to make a smaller version with a similar clamshell design.