Britain's National Grid said on Friday it had agreed to sell its Electricity System Operator (ESO) to the UK government for 630 million pounds ($827.95 million), including debt.

National Grid has struck a deal to sell its Electricity System Operator (ESO) to the government for £630m, paving the way for the division to transition into public ownership.

Shares in National Grid were down more than 10% at 10.09 pounds by 1040 GMT. Other British utilities were also down sharply on concern over political risk in the sector.