BT will end its current allocation scheme on 4 June. This has been criticised for giving BT's ADSL division an unfair advantage over competitors.
But problems with the BT-owned telecoms infrastructure are leading to 30% of ADSL installations failing, according to rival service providers and analysts.
Wholesale provider BT Ignite owns about 85% of the copper wire from local exchanges to the subscriber, but is not allowing rival providers access to information on the status of the cabling, much of which is thought to be substandard for ADSL use.
Steve Kennedy, head of future development at Thus, said, "Much of BT's copper is too old and unsuitable for ADSL services. A lot of it is aluminium which has high impedance and cross-talk characteristics, making it unsuitable for ADSL. Up to 30% of ADSL installations are failing because of these problems."
Gartner analyst Jouni Forsman confirmed roll-out problems with ADSL. "It is an issue. Service providers are having problems cleaning the loop. There is the problem with aluminium and there are also bridge taps and loop coils which degrade ADSL signals."
No-one from BT was available for comment at the time of going to press.