I've seen some of the specifications for copper drop cable that refers to it as OK to "cross" low voltage power lines - which I presume is rather different from running parallel to it.
I expect, therefore, that the spec for fibre microtubing might have similar differences. And BT's confidence in how it performs in reality might not be high.
Deploying FTTP *in the UK
* and for *mass residential use
* is relatively new, and relatively unproven. We're not talking about the technology here, but the methods of deployment, the training of the staff, and the impact of both on the future maintenance of the equipment.
So deployment of FTTP is, so far, a large-scale trial for BT to learn all the various gotcha's as they apply to the current environment in the UK, with regard to all kinds of legislation, health & safety, union rules, training and things such as weather, and the future impact to callouts and interaction with other utilities.
All of this plays it part in determining whether a FTTP rollout is profitable, or worthwhile at all, so you have to expect that they want to make sure they have learnt the right lessons as they go. If they don't, then FTTP deployment will be killed for decades...
Surely there's only one way to test the long-term resilience of an overhead fibre cable?
Yes. Both the microducting for blowing the fibre, and the fibre itself.
The manufacturer builds it to a spec.
BT install it at Martlesham Heath for a while, to see how it performs in reality. They get opinions from engineers about how it degrades over time, and how it performs in a degraded state. How maintenance is affected in a degraded state, and how a neighbour's line works when they order it ten years later.
When they're convinced it will survive for decades, and their staff can handle it, and that it deserves to be a real part of the future deployment, they can put it to the test in one or two live locations... and go through similar tests.
What they really need to ensure is that they aren't going to accidentally cause bad fragmentation of the stuff that gets deployed. If that ends up true, then they ensure they have a training nightmare in 30 years time.