UK prompt power prices rose for the third working day Monday as prompt gas prices continued to firm up and as demand was expected to increase on Tuesday, said traders.

UK OTC power for next-day delivery was trading at GBP48.40/MWh by midday, up GBP1.15 from Friday's assessment for Monday, while peak was at GBP53/MWh, up 50 pence.

On the N2EX wholesale power exchange, day-ahead baseload power cleared 66 pence higher than Friday's price for Monday, at GBP48.71/MWh.

"It's partly gas, partly demand," said a trader at a UK utility. "The system remains very comfortable."

Maximum power demand will rise by 0.5 GW to 53.2 GW on Tuesday, as temperatures decrease across the UK, boosting demand for electric heating.

Temperatures in London will be 3 degrees below the seasonal average on Tuesday, Wednesday and Thursday, and will remain a few degrees below normal until at least March 6, according to CustomWeather.

Natural gas for next-day delivery in the UK was up 0.25 pence/therm by midday to 55.35 p/th, due to the colder temperatures, said sources.

Coal-fired generation hit 21.5 GW by 1100 GMT on Monday, its highest level for this time of day since February 2, data from National Grid showed.

Gas prices have increased more than coal prices in recent days, incentivizing power companies to burn more coal for power generation.

The two reactors at Dungeness B power station will restart two days later than initially planned, forecast data from National Grid showed Monday.

Nuclear generation was pegged by National Grid at 8.5 GW Monday morning, after the Heysham 2-8 reactor in northwest England lowered output on Friday, and as three reactors were still offline for maintenance.