Virgin announced in January that its 4m customers would have their speeds doubled at no extra cost.
This was part of a network upgrade programme funded by a £110m cash injection using the "remaining proceeds" from the sale of Virgin's 50% stake in pay-TV operator UKTV last year.
In a statement today, the company said that it has now upgraded 40% of its network, and "at least doubled" the broadband speeds of many Virgin customers.
The project, due to be completed around mid-2013, means Virgin Media will offer internet speeds of 30Mbps and 60Mbps in the UK.
Customers on the top-level 100Mbps package will also see their service increase to a market-leading 120Mbps.
Jon James, the executive director of broadband at Virgin Media, said: "Virgin Media has led the greatest developments in broadband in the UK over the last decade and our 120Mb service continues to ensure that our consumers across the country get the very best that today's technology offers."
Customers will have their speeds doubled automatically as the rollout reaches their area, and they can check when they will be upgraded by visiting the 'double speed' section of Virgin Media's website.
> Virgin Media Business looks to the Generation IP future - video
> TalkTalk remains top of the Ofcom complaints list