Energy regulator Ofgem is to fine UK utility npower 2 million pounds for mishandling customer complaints, three months after it fined Centrica's British Gas over a similar breach.

Ofgem on Monday said an investigation found npower -- owned by German utility RWE -- did not provide customers with unresolved complaints key details about services offered by the energy ombudsman and that it did not have adequate policies in place to deal with complaints.

Complaint handling regulations, which took effect from October 2008, set out the service that domestic and micro-business energy customers should expect from energy companies if they raise a complaint.

The regulator, however, added npower has now addressed and remedied all the breaches of the regulations.

Consumers have a right to expect that energy companies will comply with the standards, Ofgem's senior partner for sustainable development Sarah Harrison said. npower failed to do so and although it took remedial action, it has incurred a penalty for failing consumers.

Monday's fine comes three months after the regulator fined British Gas, the country's biggest household energy supplier, 2.5 million pounds.

Ofgem is currently investigating EDF Energy for complaint handling.

The big six utilities are SSE, Centrica, Iberdrola's Scottish Power, RWE's npower, EDF Energy and E.ON UK, which recently sold its UK power networks to U.S. power firm PPL.

($1 = 0.619 British Pounds)

(Reporting by Adveith Nair; editing by Rhys Jones)