Thanks for that.. I'll attempt a restart.
Restarted apache.. same error
So restarted server.. same error.
Bizarrely.. the letsenqrypt certificate shows correctly in the domains ssl folder and identifies the domain correctly.. yet chrome browser throws up the site missmatch error and shows the cert for the actual machine name not the domain.
It really is beyond me now as everything seems correct so I've raised a ticket with bytemark.