I had been looking around for a messenger bag that can also be used as a pannier bag, as I tend to use a backpack when cycling with my laptop as I find a messenger bag moves around to much and I don't like the unevenness of the weight distribution, but then would prefer a messenger bag when i'm back on foot.

I was surprised at the lack of available options on the market but eventually found the "Frank's Dog" from an Australian company called Knog. This one (bought from chain reaction cycles) is suitable for up to 15" laptops and has a showerproof canvas outer. There is a clever pull out silver reflective rain cover in a pocket at the back, if you get caught in heavy rain. There is also a waterproof version, but I wanted something that was primarily a comfy messenger bag, that also happens to work as a pannier, rather than a pannier bag that I can carry round.

As for the pannier attachment - it fits to a socket on the back of the bag, there are also attachments available (but bought seperately) to convert it to a backpack or handlebar mount, both of which I could see as being useful.

I've yet to use it in anger, but will update this blog post if I find any problems.