The electricity company National Grid has written off �755m, reflecting a sharp decline in the value of its telecoms investments.

Nearly half of that amount was lost on the company's stake in the troubled UK telecoms carrier Energis.

Energis shares collapsed in January after the debt-laden company shocked investors by warning that slowing sales had put it at risk of breaching financing arrangements with creditors.

National Grid said it was now withdrawing from the alternative telecoms sector, but would offer infrastructure services to mobile operators.

The company is in the process of a �15bn merger with the gas pipeline group Lattice.

James Ross, the chairman of National Grid, said the tie-up would "significantly increase" the group's growth potential.

The company said its annual pre-tax profits before exceptional items rose 20% to 582 million pounds, partly because of its acquisition of the New York electricity company Niagara Mohawk.

But the telecoms write-down pushed the company to a loss of �461.7m after exceptional items for the 12 months to March, compared with profits of �617.8m last time.