Hi,

New line to be installed. No line at the moment.

Where will BT install the master socket?

I would rather put the master socket in the cupboard beneath the stairs, which would mean running a cable into the house between the two floors then along and down into the cupboard.

Do I get them to install it beneath the floor and then then extend it myself?

I will simply put the BT wifi box in the cupboard.

That is my plan anyway.

Thoughts please....

Given you'll be paying for it, I guess you can have it where you want it. I'd insist on it.

When we first had cable,TV/phone, (when Virgin was "Cable & Wireless"), from the pavement it was buried under our front border then the lawn and then to a box near the front door.
They then put a cable up the wall, neatly following the mortar line round the arch over the front door, around three sides of the house at the level of the first floor. It came in through the the bottom back corner of the lounge next to the French windows where we said we wanted it. It's quite unobtrusive, you have to look for it, otherwise you wouldn't notice it on the side of the house.