Small niche internet service providers and BT - and their customers - will be the early beneficiaries of the telecoms giant's announcement on Tuesday that it will spend £1.5bn to install new fibre-optic cables to reach the streets, and in a small number of cases the walls, of 10m homes.

The new systems, to be installed over the next five years, should be capable of speeds of up to 100 megabits per second (Mbps), though more usually up to...