The links to the Debian and Ubuntu guides are old tutorials. Today one would always use the auto-installer on Debian and Ubuntu, which installs the whole system in 10 - 15 minutes automatically: https://www.howtoforge.com/ispconfig-autoinstall-debian-ubuntu/
if that is your full zone file, you need A records for ns1 and ns2. along with glue records at your registrar. plus, what you've put for the target ip's in that zone are all private ip addresses. you should be putting the public ip address there if you want those records to be resolved externally. also, what is that mrbronz.uk in there? you realise that will actually end up resolving as mrbronz.uk.gregson.me.uk ?
Like @nhybgtvfr wrote in #43, A records for ns1 and ns2 seem to be missing. You could start reading name service tutorial, link in my signature. That should be sufficient to get name service running on your ISPConfig setup.