Both Phoenix Natural Gas and Northern Ireland Electricity are understood to be planning to announce above- inflation increases.

According to one report, the Phoenix increase could be as much as 30%, a reflection of rising international prices.

The issue is due to be ventilated at a meeting of the Assembly's enterprise committee tomorrow which is due to be addressed by Iain Osborne, the utility regulator.

Phoenix, which last March reduced tariffs by 15%, had been due to impose an annual increase in November but postponed the move, pledging not to raise tariffs until after winter. NIE Energy increased its tariffs by 3.9% in November, but there have been warnings that the rapid rise in wholesale prices might leave the company with no alternative but to carry out a mid-term review in advance of this November.

Both Phoenix and NIE are entitled by the regulator to pass through to customers any increases in wholesale costs, although the extent of any such move is subject to regulatory scrutiny,.

Home heating oil has gone up in price by at least 30% over the past year, while petrol prices have also been rising rapidly in recent months.

A spokesman for NI Authority for Utility Regulation confirmed that Mr Osborne would address the Stormont enterprise committee tomorrow morning. He said: "This briefing is expected to explain the reasons for spiralling energy costs for Northern Ireland consumers, the main drivers for NI energy prices and the role of the regulator."