OK , so it’s the case that your copper pair is delivered by poles at the front , but they put up new poles at the rear just for FTTP ?
Although a wire over the roof may be the simplest way to get the fibre cable to where your current copper service exists , as already stated it’s not an acceptable OR method , and if an OR engineer or contractor was audited on this job ( even if it were at your request ) it would be ‘failed’ and that wouldn’t be a positive outcome for the person, hence the 99% chance they would refuse to do this .
If your BT phone service is going to transfer to FTTP , the order to cease the phone line over copper , in effect also cancels the FTTC , although that is a separate order , it is linked to the FTTP order , if you refuse the FTTP install , it’s possible that the ‘cease’ order still progresses, leaving you without FTTC for a period.
There are instances of both , some don’t lose their existing service in these circumstances, and some that do there is no real way to know for sure , if the phone service isn’t being transferred to BT FTTP the chances of losing FTTC are less , but still not an absolute guarantee.
TBH , if you absolutely don’t want even the possibility of losing FTTC , you should ensure that the FTTP order has no ‘connection’ to the existing service , it would be as if you were ordering an additional service , you would then have to cease the old service manually ( yourself ) once FTTP is in , so would be paying for 2 services FTTP and FTTC for this overlapping period.
If throwing the cable over the roof is the only way you would accept FTTP provision , personally I wouldn’t order it ,as the chances are the installation wouldn’t happen , what is the reason the router at the rear of the property is unacceptable, do you have Ethernet cables running from the current router position ?
