The NBN Co will spend $4.5 billion over the next two years to provide almost 10 million households and businesses with the option of high-speed fibre connections, in a change of political direction by the Coalition government.

Years after building a controversial system which mostly used copper to connect homes to fibre nodes in the street, the government will announce on Wednesday an upgrade which will devote $3.5 billion to laying high-speed fibre cables down streets past homes.