Virgin Media is continuing its broadband speed war with BT by announcing it is doubling its access speeds for most of its four million customers.

Virgin Media will be boosting its top speed by a fifth to 120mbps for those paying for its top 100mbps. Only recently BT increased its top fibre broadband speed to 100mbps to match Virgin's.

Virgin's upgrade programme starts next month and will take 18 months to complete. Virgin customers currently on 10mbps, 20mbps, 30mbps and 50mbps packages will see their speeds at least doubled. "These speeds will ensure customers get high quality access to the huge growth in new online services," said Virgin.

Prime minister David Cameron praised Virgin's move. He said: "I welcome this announcement from Virgin Media; it will provide a great boost for the economy and change the way many households, consumers and businesses use the internet."

Virgin said the routers provided to support the upgrades are able to support broadband up to 400mbps, indicating further upgrades in the future.

Sky Broadband this week launched a new 100gbps (gigabits per second) optical backbone network to support customers downloading high definition films.