The Livingston-headquartered group said it had been helped by higher realised power prices of GBP 35.7 per megawatt hour, up GBP 10.7 from the same period the previous year.
The firm - which supplies about a fifth of Britain's energy - said boiler problems at its at Hunterston B and Hinkley Point B plants would have an impact on output for this financial year.
It said work was being carried out at both Hunterston in Ayrshire and Hinkley in Somerset to return the units to service at around 70 per cent of full capacity.
It added that a significant non-radioactive leak at its Hartlepool plant would be repaired and the plant returned to full service by December.
Bill Coley, chief executive of British Energy, said: "The first six months of the year 2006/07 have shown an improvement in financial performance compared to the first half last year largely due to higher achieved electricity prices."