Thanks for the help gents.
I had a good look around on the interweb, but never even considered looking in an online parts listing!
So, for those who find this thread in a future search, the hose appears to feed cooling water to/from the turbo and is found wrapped in a heatproof braid under the heat shield.
I looked at it for a fair while and figured I'd need to pull the exhaust manifold as a minimum; with a distinct possibility that the turbo may have to be removed too. I reckon the Mazda engineers must have started with this hose and then built the car around it!
Needless to say, I hope the hose doesn't fail before I next have the motor out or the turbo off.

At least I'll have a spare on hand!
Thanks again...