Negotiations between the ESB and unions on measures that would enable outside contractors to undertake vital transmission work could be concluded today.

Sources said last night ESB technicians had agreed yesterday on the specific measure to allow outside contractors to help with the £2 billion (€2.54 billion) upgrade programme to increase generation capacity.

Agreement on the detail of other measures, which include a 21 per cent pay rise for ESB employees and 2,000 redundancies, may be finalised later today, said the source.

Protracted negotiations have been holding up work to install five new electricity sub-stations in Dublin designed to power several Internet data centres and other high-tech industries.

A recent Government report highlighted constraints on Eirgrid due to industrial relations practices at the ESB and said the issue was one of several threatening the State's electricity supplies.