I was looking for a shoulder/cross body bag that was able to take A4 folders and ended up having a look at the Jack Wolfskin Belmont range.
Amazon had the black one for £13 when I was looking, but I didn't post it as the title called it the 'Belmont 12', but the dimensions given were seemed to be for the Belmont 20. I ordered anyway and it was the 20 litre size that i've received. The price of the black has now changed, back up to £20, but the 'Dark Berry' is now £15.57 with free delivery for Prime members. Its not quite as good a deal, but might still help someone out!