BT has postponed the upgrade of its exchanges in preparation for rollout of fibre-to-the-premises (FTTP) service as a result of technical issues.
The upgrade has been postponed from September 2011 to December 2011.
One problem faced by BT is that many of the ducts leading to homes are partially blocked, meaning BT engineers must clear them before the fibre can be laid.
The original one working day allocated for each exchange installation will not therefore be enough, and the extention may mean customers being hit with an extra engineering charge.
A BT spokesman explained that the purpose of the FTTP trial is to work out how to best roll out the infrastructure, and that the firm fully expected to encounter issues such as duct blockages.
"We sometimes have to make changes to our plans to make sure processes are sufficiently robust.
"For example, we are trialling a two-stage process to perform the external work when residents are not at home and the internal work when they are," the spokesman said.