The service will initially be rolled out in urban areas
BT's superfast broadband network will be completed in time for the 2012 Olympic Games, the firm has announced.
The £1.5bn fibre-optic network will offer speeds of up to 100 Megabits per second (Mbps) for some customers, supporting high-definition video.
However, it will only reach around 40% of homes, mainly in towns and cities.
The firm had originally said the programme would be completed by March 2013 but said the rollout was now "ahead of schedule" .
"Given the progress we're making, four million homes will have access to fibre by the end of next year," said Ian Livingston, CEO of BT.
He said the firm aims to offer 10 million homes access to the fibre network "by the time the games begin" on the 27 July.
The firm currently has five million customers.
But extending the coverage would "inevitably involve support from the public sector", he added.
Customers will be able to access the highest speeds where BT runs fibre-optic cables all the way to their home.
However, the network will still offer speeds of up to 40 Mbps in areas where the fibre cable is run to BT-owned cabinets. In these fibre-to-the-cabinet areas, homes will still be connected to the cabinets by slower copper cables.
Currently, BT's rival Virgin Media offers some homes broadband speeds of up to 50 Mbps, regarded as super-fast broadband.
The UK government has said it wants super-fast broadband available to 90% of the country by the end of 2017 and everyone in the country to have access to broadband speeds of 2 Mbps by 2012.
However, Mr Livingston called for further clarity from the UK government.
"If you look around the world, several governments are pro-actively supporting the roll out of fibre broadband," he said.
"There's still a debate in the UK - which is fine - but we need our politicians to decide how much of a priority fibre broadband is."
The government plans to introduce an annual tax of £6 to fund the rollout of broadband, particularly for rural areas.