National Grid owns and operates Britain's main gas network and the high-voltage electricity transmission network in England and Wales, managing flows of power onto and around the grids.

It also owns interconnectors, which import power from continental Europe, and the UK's electricity infrastructure.

Different companies own regional distribution networks which carry electricity at lower voltages from the main grid via powerlines, cables and substations to homes and businesses.

There are similar regional distribution networks for gas, carrying it at ever lower pressure until it reaches customers.

British lawmakers on parliament's Energy and Climate Change committee said in a report the system needed to be changed so regional distributors could control power flows on their networks better, as more renewable power is generated locally.

Most of Britain's solar power is connected to local distribution networks and cannot be seen at the overall level, the report said. Instead, it is measured only as a reduction in the demand for power rather than as an input.

The report said smart grid technology would enable distribution network operators to move from a passive role to being responsible for balancing energy flows, effectively becoming system operators at a local level.

The committee said National Grid has conflicts of interest because it owns assets which bring in power, but also operates the system which buys the power from those assets.

"National Grid's technical expertise in operating the national energy system must be weighed against its potential conflicts of interest," said Agnus Brendan McNeil, chairman of the committee, which called for the creation of an Independent System Operator (ISO).

In the United States, an ISO coordinates, controls and monitors the operation of an electrical power system in one state or sometimes several states. Regional transmission organisations do the same, but cover a larger geography.

National Grid shares were 0.9 percent lower at 953.1 pence at 0814 GMT.

A National Grid spokeswoman said there was little evidence that the ISO model would provide any benefits which would justify the cost to households, potential disruption and the risks to security of supply.

"We are currently working with the Government and with regulators to ensure we continue to manage potential conflicts as our role develops," she added.

(Editing by David Clarke and Alexander Smith)

By Nina Chestney