Good evening,
After a lot of work put in by CaptainKostaZ over several days, we've finally managed to resolve the connectivity issue.
I will leave the solution to be presented by him/the team shortly but I've now managed to get into both ATS and ETS through the launcher (downloading the required updates, etc.) and successfully logged in to a server in each game.
Many thanks for the dedicated support.
See you on the road.
Vulcan