Auditors, Ernst & Young (E&Y), said Tuesday that Britain will need £234 billion ($334 billion) investments in new energy infrastructure in order to meet carbon reduction and renewable energy targets set for 2020. A study carried out by the auditors also warned that available investment could move on to different sectors or projects abroad if energy companies failed to reassure investors about future returns.

In a study for large UK-based multinational utility Centrica, Ernst & Young said the level of investment needed was double the value of the UK's total energy supply asset base.

"The landscape in which this investment must be raised has altered fundamentally as the credit crunch and economic down turn take hold," the report said.

Centrica commissioned Ernst & Young to update its 2008 ''Costing the Earth'' study, published last summer, which looked at the cost implications for UK energy customers of meeting carbon emissions and renewable energy targets by 2020.

This previous study had estimated costs at £165 billion.

The new study, ''Securing the UK's energy future--meeting the financing challenge,'' reflects increased development costs for energy projects over an extended period to 2025. It includes capital costs for new nuclear and renewables capacity, plus the cost of increased levels of gas storage and import infrastructure.

Ernst & Young estimates that the energy supply industry will need to earn an annualized return on invested capital (pre-tax) of around 12% for the three years post construction (2026-28) on the £234 billion of new investment.

This is in line with returns made by the industry in recent years, which averaged 12% from 2005-07 (pre-tax).

Steve Jennings, partner and head of Ernst & Young's power and utilities team, said securing the investment "will rely upon energy companies' ability to access debt and equity finance. They must be able to persuade their lenders and shareholders that income on new assets will be enough to service and repay the debt and provide sustainable shareholder returns."

There was a risk that investment could migrate to other sectors and/or other countries, Jennings said. "The energy supply industry would need to play its role in funding the new investment in the most efficient way," he said, "for example through optimizing financing costs, operating expenditure, tax liabilities and capital expenditure programs."