|The following appears to have done what I need:|
on the existing server, under 'namesrevers' tab, add the new name server.
on the existing server, under 'zone transfer' ensure that transers are permitted to only the servers on the name servers tab
on the new server, create a new secondary zone.
add the ip address of the current master server.
I did initially create a secondary but had an error message saying it couldn't load the zone from the master, I obviously missed a few setting on the existing server.
I must have also misintrepeted some sites where I thought I read you could only replicate a AD integrated DNS to another DC.