Thanks all for the very helpful replies and pics. I feel ready to rebook the installation.
Do the engineers make up the cable on site to suit the distance from entry point to ONT? Ideal location of the ONT here is about 1.8 m from the entry point; I’m hoping that’s viable.
The internal cable is pre-made at one end , the end that plugs into the ONT , ( it’s an SC/APC connector ) these cables are supplied in various lengths , so the appropriate size selected by the installer ( obviously the one that’s slightly bigger than the length of the internal cable run ) and at the CSP this cable cut to the correct length , it’s then spliced to the external fibre cable and the excess coiled around the mandrel inside the CSP , it’s not really like a patch cord as that would have plugs at both ends , OR did experiment with field fit connections( so the tech fitted the SC/APC plug ) but they had a high failure rate and were discontinued
When they installed mine they just drilled about a 5mm hole from the back of the CSP, just enough to get the tail of the fibre through from the ONT , very neat.
I also had a POE Ethernet feed with a 12v converter on the end so didn't need a mains socket but I had an extension lead available just in case.
It appears that Openreach engineers carry a variety of lengths up to 30m to connect the CSP to the ONT.
https://forums.thinkbroadband.com/fibre/4717372-length-of-insideoutside-cable-that-openreach-will-in...
Some useful details here:
https://www.openreach.co.uk/cpportal/products/fibre-broadband/installation-options
A quick update - installation went fine. Tellingly the engineer put the fibre optic straight through the wall without the liner or internal cover so the cable runs straight into ONT. I provided the hook to fly the cable outside from telegraph pole to the house (OR approved) - he said he’d used his last one on the previous job 😳. Anyway, I got the routing I wanted and he was attentive to my requests. Here’s the internal arrangement- a bit of filler where optical cable enters the house and I’ll match paint the filler to cover it up.
Openreach turned up for the 4th attempt at FTTP. They were very good. Used the existing hole in the external brickwork for the fibre cable, with no plastic sheath so didn’t have to enlarge the hole to accommodate it, and didn’t fit one of those neat internal point-of-exit caps with its 15mm housing in the wall - the cable just emerges as in the pic above, and I’ve used a bit of filler likewise. I’m not particularly bothered, as the exit point is now concealed - boxed in along with the cable for the spur to the new double socket.