Thank you Owen I was hoping you'd answer. Two votes for Ortlieb - hopefully I haven't errored by opting for the OS map case instead (on account of it being bigger so I thought better able to accommodate the weatherproof maps).
I can tolerate things hanging round my neck but I have to admit I hadn't considered just stuffing it down the hip strap. Maybe this was £20 I didn't need to spend!
Ninthace, I tried printing an A4 map of my last walk and I found it didn't contain enough detail to be of any use nor did it have grid lines to orient the compass bezel to or take grid references from. I don't know what you do differently, it's obvious you don't do what I did.