Having checked out the pictures of the official case I realise that Nokia are not going to come through with what I want.

My interim solution is to reduce the width of the included pouch by 1cm. After trimming off the excess material I now have a soft slip-on case which doesn’t permit the device to slip out inadvertently.

It will serve as a template if I come across a sheet of neoprene or similar, i.e. rubberised on the outside and soft lining inside.