You're not wrong about the copper issues and it's not just Forest Hill, it's over a wide area of South London. It could be worse though! I used to live in Camberwell which is fed by the Brixton exchange and one of the longest cable lengths in London... the most they could supply there was 4 Mb!

I'm an IT Consultant (though not a telecoms engineer) and it was my understanding that FTTC and FTTP were essentially compatible and that upgrading from FTTC to FTTP involved fitting new equipment at the cabinet and running the new fibre line to the premises? Hence why BT talks about getting the 40Mbps Infinity service out to customers with an eye on the 100Mbps upgrade for the future. They wouldn't waste running the FTTC infrastructure if it weren't upgradable to FTTP without running new lines- surely?!?