Plusnet has admitted that around five per cent of broadband subscribers recently migrated to a new LLU platform lost their connection.
The ISP is piggybacking on Tiscali's LLU network to provide services up to 8 meg and last week transferred around 1,000 punters to the unbundled service.
But a problem at three London exchanges meant that 44 customers were left without broadband.
A spokesman for the Sheffield-based ISP told El Reg that the problem was due to a snag with the "interface between Plusnet and Tiscali's systems".
"We have about 30 of the 44 customers back online and we're hoping to have all 44 on by the end of today," he told us. ®