Would the meter be inside the cabinet? Or in some ground inspection pit?
If the former, then it still means that the tails (before cabinet installation) would be unmetered.
I just found a post suggesting that the meter is in the cabinet, and remotely-readable:
cabinet power supply
As you point out - the correctly sealed termination, into a meter, inside the cabinet - seems to me to make it impossible to install power until the cabinet is physically present.
Combined with the attitudes seen in that report, I'm comfortable in believing that BT don't order power until the cabinet is *actually* in place.