I am getting the impression my hunches may have been correct, re overlap of smart meter and homeplug power line comms technologies.
I have no idea whether this is relevant to any current or planned UK smart meter roll out, but there does seem to be an emerging homeplug technology
'Homeplug Green PHY', aimed at the smart meter industry as well as other 'green' industries.
And if I understand correctly, it involves high speed power line comms within the home. Though I can't comment on how it would co-exist with vdsl, that would be pure speculation.
Purely as example, see following from qualcomm...
http://www.qca.qualcomm.com/ioe/homeplugr-green-phy