Some notes so that I remember what I did!

Domain Name

I purchased the domain name from 123-reg

Cloudflare

Configured a free account on Cloudflare Using the 123-reg management portal, changed the nameservers to use the Cloudflare ones

Git Hub Pages

Set the custom domain name against the DavidBetteridge.github.io repro to be davidbetteridge.net

Using the Cloudflare management portal created 'A' records to point at github

Site became available straight away