Virgin Media has launched an internal investigation and suspended four members of staff over concerns that progress on £3bn network expansion work had been "misrepresented".
The cable operator's parent firm Liberty Global said it was discovered in February that 142,000 homes and businesses set to be connected to Virgin's network needed more work than had been stated before.
Four Virgin Media employees have been suspended and removed from their posts, while investigations are ongoing. Liberty Global said pending the results of those, disciplinary action may be taken against employees, including dismissal.
The firm said it discovered in February that the construction work "had not progressed as originally understood" and then initiated a review of the records underlying the construction status of the inactive premises, as well as the circumstances that led to "the overstatement" of construction progress.
Liberty Global had believed construction work to lay new cables was predominantly complete and that the new lines only required power and plugging into its street cabinets, work it told investors would be complete in the first quarter of 2017.
It now expects all these premises to be connected by 30 June this year.
Virgin Media is investing £3bn to extend its ultrafast fibre broadband network to an additional four million premises in Project Lightning, to reach a total of 17m homes and businesses by the end of 2019.
The 142,000 are a small proportion of the programme; some 323,000 homes and firms were connected last year. Liberty Global plans to connect 1.3m-1.4m across Europe this year and of that Virgin Media expects to connect 700,000 to 800,000 premises pursuant to Project Lightning.
Liberty Global told investors it did not feel shortfall during the early part of the year "will have any impact on the total number of premises that we expect to add pursuant to the overall Project Lightning programme".
It has also announced a rejigging of of management, with Robert Evans being appointed Project Lightning's managing director. He will jointly report to Balan Nair, Liberty Global's chief technology and innovation officer, and Tom Mockridge, Virgin Media's chief executive.