you are probably limited by the contract you are on rather than any actual limitations, so I would think you could ask them for a faster rate.
The BT contract is the daughter's. BT is her employer (although she work's for the Police), and the broadband comes free with the job. I've no idea what limitations might be in place, but I'll mention it to her.
You've all given me plenty of options to think about. Seems that fibre is good, but cable, with a network switch near the middle, will also work.
One problem with a single piece of pre terminated fibre is that it will have to pass through two 600mm thick solid stone boundary walls between properties. These walls have 20mm round PVC conduit through them that was fitted when the renovations were done, and have Cat5E, bell wire, and 2 pair 'phone cable passing through them. Plenty of room for more Cat5E or 6, but those optical plugs are going to be a problem.
45m of Cat5E/6 followed by 100m of fibre is possible, or is that pointless?
As far as the trench is concerned (still another 30m to dig), I've ordered some green 65mm outside/50mm inside smooth bored twinwall duct to go in with the SWA and 20mm water pipe, so that kicks the final decision down the road for a week or two.
10mm2 3C for the SWA turns out to be just too small. Considered 6mm2 5C doubled up, which is just adequate, but will probably go with 16mm2 3C and have done with it. Costs another £100 on top of the 6mm2, but that's minor compared to what the whole project is costing.