Thanks for the follow-up.
My local network is 192.168.1.* so even if I set the EV3 IP address to 10.0.1.1 I can’t ping it because 10.*.*.* isn’t my local network.
When I set the Ev3 to 192.168.1.13 (accessible on my local network) I can ping it.
When I try and connect with SFTP it says “Server rejected SFTP but it listens for FTP connections”.
When I try and connect with FTP it says “No connection could be made because the target machine actively rejected it”.
When I try and connect with SCP it says “Connection to 192.168.1.13 refused”.
So: It’s definitely there and listening.
It seems that the network setup is correct but the brick is refusing to talk.
Seeing as it’s listening, why would 10.0.1.1 be any different to 192.168.1.13?