Great Britain’s energy system operator has warned that “extreme temperatures” could hit power supplies on Thursday night, as the UK entered its third heatwave of the year.

The National Energy System Operator (Neso) issued a notice overnight asking for extra supplies from power generators to cope with the added demand from households turning on fans and air conditioners to cope with the high temperatures.

It comes only weeks after Neso issued pleas for extra electricity during last month’s heatwave, when the UK recorded a provisional high of 37.7C at Lingwood in Norfolk on Friday 27 June, smashing the previous June record of 35.6C, set in 1976.

Parts of southern England are likely to hit highs of 34C on Thursday, and while temperatures are expected to stay below June’s record-breaking levels, the hot weather is due to last much longer, dragging out over 10 days.

In a statement, Neso said it was “giving participants the opportunity to make any additional generation or flexibility available during the forecast period.

“Our forecasts indicate tight electricity margins during tomorrow [Thursday] evening’s peak period,” the operator said. “This is due to extreme temperatures across Europe, reducing the availability of some generation.”

However, the government-owned body added that its “electricity margin notice” was a routine tool used to balance the electricity system. “We will continue to monitor conditions closely and take any actions necessary to maintain secure electricity supplies,” it added. “There is no risk to customer electricity supplies.”

While households are not expected to experience any supply interruptions, the notice raises the prospect of Neso again paying much higher than average prices to gas power plants to ensure electricity demand is met.

Across the Channel, the French state-owned utility company EDF warned that the latest heatwave was putting a strain on its nuclear reactors, which regularly export power to the UK and Germany.

The company said output could be curbed at up to five of its nuclear plants in the coming days, as hot weather affects the temperature of river water used to cool its reactors. It will start by reducing production and using only two reactors this week, although it could be the first in a series of slowdowns as the heatwave moves across the continent.

Western Europe is entering its third heatwave in six weeks, sparking wildfires in France and Spain. In France, where 35,400 hectares (87,474 acres) have already burned, double the average in Spain, where 55,128 hectares have been scorched, according to the European Forest Fire Information System.