We recently had a Virgin engineer turn up at home, stating that there were problems in the neighbourhood with broadband.
My wife let him in and he adjusted something on the back of the home hub, and also outside.
Funny mean to sound paranoid, but in all the years I've been with Virgin, I've never known them to do protective works. He said that none of the broadband has been set up correctly and they were going around adjusting everyone's settings.
Welcome to the forums, It sounds like there was an area issue which the engineers may occasionally need access for.
I have taken a look and it seems there is an issue with FECS (noise) in your area. I have raised this to networks to investigate further. I will let you know once I know more. But it is likely this is what the engineer was originally looking for.