I would like to point out that to the best of my knowledge VM techs are supposed to be avoiding the use of attenuators where possible anyway. Normally they should be using the correct tap point at the street cab so that the power levels fall with in the ideal range by the time it gets to your house. (different tap points have different attenuations to support how close the houses are to the street cab itself).
As a Very Insightful Person, I'm here to share my knowledge. I don't work for Virgin Media.