Virgin Media is to spend £110m on the 18-month upgrade programme.
The company says that those who subscribe to its up to 10Mb service – 74% of its 4.1m internet subscribers – will see their speed double to 20Mb.
Those on its up to 20Mb tier, 12% of the total subscriber base, will see their speed tripled to 60Mb.
The 9% who take 30Mb broadband will rise to 60Mb.
And the 5% who take services from 50Mb to 100Mb will rise to a speed of between 100Mb and 120Mb.
The top-tier speed – at 120Mb it will be the quickest offered in the UK – will enable customers to download a high-definition movie in about five minutes.
"As people are increasingly doing more online, and getting connected to the internet with lots of different devices, having a fast, reliable broadband service should not be a luxury," said Neil Berkett, the chief executive of Virgin Media.
"We want to make sure that consumers have access to the best value broadband service and that means a superfast connection."
Virgin Media intends to mostly fund the programme with the remaining £100m of the proceeds of the sale of its 50% stake in UKTV to US TV company Scripps.