Sony has release the 30.1.B.1.46 software update for the Xperia M5 and M5 Dual. If you were expecting Android Marshmallow, we're sorry to disappoint you. The update simply includes the January Android security update bug fixes which should fix inadvertent shutdowns of the phone.
UK residents can pre-order the new Xperia M5 direct from select retailers. It looks like Carphone Warehouse has exclusive rights in the region to the Gold variant.
We're being told that this product will be in stores and ship by February 8th.