Is this type of work covered by a similar set of written regulations that DNO's follow
The Electricity Act 1989 and The Electricity Safety, Quality and Continuity Regulations 2002 (which forms part of it)
How the DNOs comply with these is in the main up to each DNO, though some guidence is given in documents from the Energy Networks Association. (though I can't find one for this scenario)
There is no equivalent to BS7671, as B-A-S posted the cable belongs to the DNO and it is their choice how it is installed.
(Part P only says that it must be safe without saying how! Though BS7671 is one way of acieving safety. The Act covering the DNOs is the same, it does not specify how safety should be achieved)
It also concerns me that the service goes from a pole to a bungalow, it is likely that this will not comply with the overhead line clearences required by ESQCR, in which case it must be undergrounded (though this may give you a negotiating position regarding the costs)