If there's already a wayleave in place then your daughter (and/or the property owner, if different) is entitled to a very small annual payment. (If it's just a single power line the payment is of the order of a couple of quid. A pole in the garden might take that up to around £30).
If there's no wayleave in place then
(a) a wayleave can be sought and obtained (but, as stated above, it won't yield a lot of money) ; and
(b) compensation can be sought for the loss of value to the property, suffered by the owner, due to the presence of the cable.
It's the compensation element that Thomas Broadbent are interested in but, in order to get it, the owner (or the owner's agent, such as TB) has to show that the owner has suffered a genuine loss. It's unlikely that any loss to the value of the property could be established if the cables were already in place when the property was purchased.
This thread
might be relevant here:
http://forums.moneysavingexpert.com/showthread.php?p=11414843