British officials say the country may need as much as $173 billion in power plant investments during the next decade to ensure electricity supplies are adequate.
Paul Massara, RWE's representative in the United Kingdom, told The Daily Telegraph newspaper there was "a huge amount of detail" missing from a government energy plan for power plant investments.
"If you want to get those guys (private investors) involved you have to provide long-term certainty and clarity of purpose and that's what's so desperately needed," he was quoted as saying.
Britain last year announced plans to finance new nuclear and renewable energy facilities in a way that would run counter to EU efforts to restrict government aid.
RWE and counterpart E.ON last year backed out of a $24 billion nuclear program in the country, saying a German decision to back away from nuclear power made it a tough energy policy to pursue.
Massara said he doubted there would be major investments in the British energy sector "unless there are propositions which attract not only us but also enable other capital lenders to come into the market place."