Days after it was revealed that millions of UK homes can only get broadband speeds of less than 2Mbit/s, BT has finally announced it will roll out ADSL2+ technology to all its consumer and business customers, free of charge.

ADSL2+ technology was first used by an ISP to offer London customers broadband speeds of 24Mbit/s nearly four years ago. This triggered a rush of rival ISPs to install their own DSLAMS into BT's exchanges in order to offer users an unbundled service with much better line speeds that could be achieved via BT's own wholesale service, which currently maxes out at 8Mbit/s (although of course, many UK homes and businesses get nowhere near this figure).

BT said that it had successfully trialled the ADSL2+ technology, which initially started in the Midlands, but then broadened it out across enabled exchanges to include 60,000 customers. It plans to start rolling out ADSL2+ to all of its consumer and business customers.

549 telephone exchanges will benefit from the technology initially, which serve around 40 percent (or 10 million) of the homes in the UK. BT hopes that the service would reach 55 percent of British homes by 2010, depending upon consumer demand.

"We are advertising the service as an 'up to 20Mbit/s' service because, although 24Mbit/s can technically be delivered, we believe the numbers of customers who could potentially receive up to 24Mbit/s is very small and it would be misleading to advertise the service as such," said BT in an email to Techworld. "We will give each customer a speed estimate before they order the service."

But how many customers will actually get to experience the upper speed levels that ADSL2+ can offer?

"Every end user line is different and can be affected by a variety of factors including distance from the exchange, internal wiring, interference from electrical appliances and other factors," said BT.

"We use the theoretical maximum speed the exchange technology can support as shorthand to describe a broadband service - the so called 'up to' speeds," it said. "In this case, up to 20Mbit/s."

"BT Retail customers will have an individual line speed estimate based upon the unique characteristics of their line before they place an order or re-contract," said BT. "We have not set a target average speed at this stage. However, our trials show that the average customer shows a significant increase in speed in both directions."

BT thinks that consumers would see an increase in upload speed of up to 1Mbit/s. BT also said it plans to offer its I-Plate (or Broadband Accelerator as it is also known), which eliminates electrical interference from telephone-extension wiring to improve broadband speeds and reliability, free of charge to some customers.

"Unlike other providers, BT is upgrading customers to 20Mbit/s for free," said Gavin Patterson, CEO of BT Retail in a statement. "In line with the Government's Digital Britain review, we will be making higher speeds more widely available."

In a separate move, BT Retail will begin the first trials of up to 40Mbit/s fibre-based broadband in Whitchurch, South Wales and Muswell Hill, London this summer.