BT Infinity is a broadband service in the United Kingdom provided by BT Retail, the consumer sales arm of the BT Group. The underlying network is fibre-to-the-cabinet (FTTC), which uses optical fibre for all except the final few hundred metres to the consumer, and delivers claimed download speeds of "up to 76 Mbit/s" and upload speeds of "up to 19 Mbit/s" depending on package selected. The fibre terminates in a new roadside cabinet containing a DSLAM, from where the final connection to the customer uses VDSL2 technology.
Unlike ADSL which typically delivers far lower speeds than the maximum headline speed marketed, BT Infinity usually delivers very close to the maximum possible. While no reliable results for the new 76 Mbit/s service are available, the previous up to 40 Mbit/s service (now rebranded as up to 38Mbit/s) has been shown to deliver a median speed of 38 Mbit/s.
An additional full fibre-to-the-home service which uses GPON technology instead is also offered under the BT Infinity brand. This service is expected to reach 300 Mbit/s download speeds in 2012 though this is only available in limited areas.
Following a technical trial involving 50 homes in Foxhall, Ipswich, in January 2009, and operational pilots at the Muswell Hill, Whitchurch and Glasgow Halfway telephone exchanges, the service was launched commercially on 25 January 2010. When it was announced, BT expected 4 million customers for the service by the end of the year. Infinity forms part of BT's £1.5bn plan to make superfast broadband available to 40% of the UK by the summer of 2012, using FTTC and FTTP services. Previously, the only major provider of domestic fibre optic broadband in the UK was Virgin Media's hybrid fibre-coaxial service.
BT Retail ran a competition called "Race to Infinity" in the autumn of 2010 to assess demand for the Infinity product in 2495 mostly-rural communities. The winners would be the 5 areas served by a telephone exchange that received the most percentage votes out of its "total connections" by 31 December 2010.
BT announced on 3 January 2011 that 6, not the originally planned 5, areas would receive Infinity by early 2012. The six winning areas were: Whitchurch, Hampshire (104%); Caxton, Cambridgeshire (103%); Madingley, Cambridgeshire (102%); Innerleithen, Scottish Borders (101%); Blewbury, Oxfordshire (99.8%); Baschurch, Shropshire (95%).
Voting surpassed 100% in several areas because new places had been built and residents without landlines connected to the area's exchange could vote - and were encouraged to do so by very active locally-run volunteer campaigns.
In addition to winning Infinity, each of the six winning areas are to receive £5,000 of computer equipment for a local community project. BT originally planned on awarding the prize to just 1 of the top 5 winners.
An area's exchange had to get a minimum of 1,000 votes in order to enter the competition; any area whose exchange reached 75% would be actively engaged with by BT for an upgrade. Two exchanges outside the top 6 winners achieved over 75%: Marton, Warwickshire; and Capel, Surrey.
On 2 February 2011, BT announced that all 10 exchanges would be upgraded.
In March 2012, BT announced that they would be upgrading all of their packages to take advantage of their newer and much faster 100Mbit/s fibre-optic technology. Areas are expected to be upgraded within the upcoming months.
On 25 September, 2012, BT announced 163 new fibre exchanges. They are all expected to be activated sometime during 2013. Among the list, is Blackpool, Lancashire, Desford, Leicestershire, Earl Shilton, Leicestershire, Oakengates, Shropshire, Skegness, Torquay, Cowdenbeath, Fife, Christchurch, Dorset, Buckhaven, Fife and Dursley.
In December 2012, BT had begun the first real-world tests of newer XGPON technology, developed by BT and ZTE collectively, to allow superfast fibre-optic broadband up to 10Gbit/s (10,000Mbit/s). The testing is currently being held at Arcol UK in Cornwall and will operate in tandem with its current 330Mbit/s downlink package.
On 13 February, 2013, BT announced 99 new fibre exchanges. They are all expected to be activated by the end of 2014. Among the list, is Beamish, Birtley, Tyne and Wear, Darlington, Coatbridge, Grimsby and Yapton.
BT have received objections to the siting of various road-side boxes that are being installed for BT Infinity. Objectors are not opposed to the new technology, but propose that better locations could be found for the boxes. The green BT Infinity boxes are similar to existing street side cabinets but are taller and wider than existing units, with some models being 1.6 metres (5.2 ft) tall.
BT has also being widely criticised for upgrading telephone exchanges to support BT Infinity but then failing to upgrade all 'less profitable' cabinets. BT does not make cabinet upgrade plans public knowledge.  
National Security Threats & Personal Privacy
BT notified the UK government in 2003 of Huawei's interest on their £10b network upgrade contract, part of which (for network equipment) was awarded to Huawei in 2005. Between 2010 and 2012 the UK intelligence community initiated an investigation aimed at the foreign supplier of BT's new Infinity fibre infrastructure Huawei with increasing urgency after the USA, Canada and Australia prevented the company from operating in their countries.  On 16 December 2012 David Cameron was supplied with a in-depth report indicating that the intelligence services have very grave doubts regarding Huawei, that the UK governmental, military, business community and private citizen's privacy may be under serious threat, as a result BT's Infinity program and other projects are now to come under urgent review.
On 7th June 2013, British law makers concluded that BT should never have allowed the Chinese company access to the UK's critical communications network without ministerial oversight, saying they were 'deeply shocked' that BT did not bother to inform government they were allowing Huawei and ZTE, both foreign entities with ties to the Chinese military unfettered access to critical national systems. Furthermore, ministers discovered that the agency with responsibility to ensure Chinese equipment and code was threat-free was entirely staffed by Huawei employees. Subsequently, parliamentarians confirmed that in case of an attack on the UK there was nothing at this point that could done to stop Chinese infiltration attacking critical national infrastructure.
Another Chinese company ZTE supplying extensive network equipment and subscriber hardware to BT Infinity is also under scrutiny after the US, Canada, Australia and the European Union declared the company a security risk to its citizens. 
- BT Infinity Product Page BT Retail, accessed 2012-04-21
- UK fixed-line broadband performance, November 2011 Office of Communications, Published 2012-02-02, Accessed 20120-04-21
- BT announce 300Meg speeds for FTTH are coming in the spring Thinkbroadband, accessed 2012-04-21
- Superfast Broadband Programme Update, BT, published June 2009, accessed 2010-10-27
- BT launches new Infinity broadband service V3, published 2010-01-21, accessed 2010-10-27
- BT launches BT Infinity superfast broadband at a competitive price BT, published 2010-01-21, accessed 2010-10-27
- BT Infinity Fibre Optic Broadband Comparison, accessed 2010-10-27
- Ofcom | Supporting the UK’s super-fast broadband future, published 10-10-07, accessed 10-10-27
- Race to Infinity Retrieved 11 January 2011
- "BT broadband race winners announced", BBC
- "WE WON! Top in the UK for Rural Broadband!", Whitchurch.org.uk
- "…and now we WIN £5000!", Whitchurch.org.uk
- "BT Expands Free UK Superfast Broadband Upgrade from 6 to 10 Communities", ISPreview
- "BT announces 163 new fibre exchanges", Techbeast.net
- Updated 20:23 23 Nov 2012 by Chris Smith (2012-11-23). "BT trialling 10-gigabit per second broadband in Cornwall". T3. Retrieved 2013-07-04.
- ""BT reveals latest phase of fibre roll-out"". Btplc.com. Retrieved 2013-07-04.
- conservationists battle bt over broadband cabinets, published 2 July 2010, accessed 11-11-2010
- The BT broadband boxes that have muzzled the Muswell Hill fibre trial, published 1 September 2010, accessed 11-11-2010
- BT Infinity ‘Blackspots’ & Why No Fibre Optic For Me! Accessed 18 July 2013.
- Why doesn’t BT come clean over fibre cabinet notspots? Accessed 18 July 2013.
- Charles Arthur (2012-10-08). "China's Huawei and ZTE pose national security threat, says US committee | Technology | guardian.co.uk". Guardian. Retrieved 2013-07-04.
- Cusick, James (16 DECEMBER 2012). "China telecoms giant could be cyber-security risk to Britain". The Independent.
- Sandle, Paul (2013-06-07). "Parliamentarians say Huawei-BT deal exposes flawed security controls | Reuters". Uk.reuters.com. Retrieved 2013-07-04.
- Shead, Sam (2012-12-13). "Huawei and ZTE could pose security and business threat to Europe, says EU report". ZDNet. Retrieved 2013-07-04.