Thanks for you kind assistance and advice but sadly my dns knowledge appears limited - probably because the dns magic just happens on the bytemark system. I have a test domain registered with 123 reg with the nameservers set to point at ns1.mythic-beasts.com and ns2.mythic-beasts.com - with bytemark this is really all that’s requried to get up and running 
What further steps do I need to take so that I can get the site (hosed on mythic servers) to display? Please assume that I have zero knowledge in your response.