The local loop is the landline telephone line that loops from a customers premises to the telephone exchange. The telephone exchange has equipment, usually owned by BT Wholesale, that provides broadband services -- such as a DSLAM (Digital Subscriber Line Access Multiplexer) -- and plain old telephone services (POTS). There is in the region of 5500-5600 telephone exchanges in the UK, and these facilitates have a combination of equipment from BT Wholesale and LLC operators. Local Loop Unbundling (LLU) operators are telecommunications companies who install their own equipment -- so they don't have to rent BT's -- at the telephone exchange; which means LLU operators have complete control over their own network, and they can also provide wholesale services to other ISP's and medium/large businesses.
Local telephone line that loops to the telephone exchange
Many Internet Service Providers (ISP) -- who operate in the UK -- are simple reselling the service of a larger ISP. Genuinely independent ISP's, who control their own network, are fairly rare: due to the cost of installing and maintaining their own network equipment at telephone exchanges. Some of the largest LLU operators in the UK are: Edge Telecom, Entanet, Fluency, Kingston, Node4, Orbital, Origin Broadband, Redcentric, Sky, Spectrum, TalkTalk, Timico Partners, Vodafone and Zen Internet. LLU operators do not necessarily install equipment at every telephone exchange, and some LLU operators, like Entanet, sell wholesale to ISP's (BT Wholesale alternative) and offer "reseller packaged broadband". The largest LLU operators -- who are located at the most telephone exchanges -- are probably: Sky, TalkTalk and Vodafone.
The equipment installed by BT and LLU operators at telephone exchanges is always changing and being updated. In 2013, BT stated that it planned to remove the majority of its 20th Century Network (20CN) equipment from exchanges by 2016. The problem with 20th Century Network (20CN) ADSL equipment is that it can only provide 8Mbps; while a reasonable speed, most rural areas can get nowhere near 8Mbps due to their distance from the exchange. BT plan to replace their 20th Century Network (20CN) ADSL equipment with a 21CN Broadband service: which is a combination of optic fibre and ADSL2+ (24Mbps) technologies; both of which will provide considerable higher speeds in rural areas. Timico, an LLU operator, who provides managed Cloud services, were also migrating customers from 20CN services to 21CN services, during 2013.
Opening up telephone exchanges to LLU operators is believed to improve competition, and there is also the belief that where LLU competition is high, its more likely that equipment will be upgraded (especially for rural areas).