[Puppet Users] Hostname wildcards in module

I'm new to Puppet (yay!) and working through having a different resolv.conf
for systems that contain a certain string in their hostname.

I've got the following in my modules/system/files.pp:

class system::files {
case $hostname {
/^uklab*$/: {
$file = "resolv-isg.conf"
}
default: {
$file = "resolv-internal.conf"
}
}

file { '/etc/resolv.conf':
source => "puppet:///modules/system/$file"
}
}

For some reason it always uses the default, what am I doing wrong? I've
done loads of Googling around but can't seem to find a reasonable answer. I
know I could use a different module per node but didn't want to have loads
of per-node nodules but is this the only way?