Moving external box

VM staff won't go into a loft, unless it's been converted into a living space. 

This will need close liaison with VM as extension of fibre is not straightforward.  It will likely have to be resupplied from the pole to the nominated location.  You'll be without VM broadband for the works duration - and don't hold your breath for the loft; an upstairs bedroom may be your best bet, all done before you do the house extension.

You need to prepare much of this in advance, so you are in control of the process.

We had FTTP installed recently. I had drilled a hole through the cavity wall just below the soffit, and into the bedroom above a fitted wardrobe. I left a trace wire for the Openreach man to pull the fibre through. The 'external' box is inside, next to the ONT.  There is of course an external wall fixing to take the strain of the long external cable.

The Openreach guy turned up exactly on time and left in a couple of hours with the connection already working. 

Do not assume a replacement fibre from a pole will cost the regular £25 for a no-fault job, and I suspect it will be substantially more.

We're assuming the fibre has to be extended.

Depending on the new fixing location and the angle of run from the pole, the existing fibre might be long enough and just need moving at the house end.