Within day gas fell by 2.20 pence to 29.50 pence per therm by 0915 GMT Day-ahead gas was 1.15 pence lower at 30.50 pence per therm.

The system was oversupplied by 16 million cubic metres (mcm), with demand forecast at 119.7 mcm and supply at 135.6 mcm per day, National Grid data showed.

The oversupply is due to some fields supplying UK gas terminals coming to the end of maintenance outages and slowly ramping up, Refintiv analysts said in a morning note.

"Bacton Seal is up by 7 mcm and Teesside CATS up by 4 mcm," they added.

Total gas flows from UK production fields are expected at 92 mcm, around 14 mcm higher than Friday.

Wind generation is expected to be around 6 gigawatts (GW) on Monday and Tuesday, Elexon data showed, out of a total metered capacity of around 12 GW.

On demand side, gas-for-power demand is expected at around 36 mcm on Monday, edging down to 34 mcm on Tuesday, Refinitiv Eikon data showed. These are lower forecasts than expected earlier.

Sources said that bearish drivers are prevailing now after a short squeeze that lifted prices late last week.

Ongoing maintenance is a "tad supportive," but fundamentals are bearish and current volumes are also very thin, an analyst source said.

"Parties who were short have closed short," a gas trader said. "Now we are back to basics - fundamental drivers," he said, adding that full storages and likely more oversupply after Norway's Troll field comes back online.

UK September contract dropped by 0.82 p to 31.90 p/therm.

Dutch day-ahead gas fell by 0.55 euro to 10.75 euros per megawatt hour.

Dutch September contract down 0.33 euro to 11.65 euros/MWh.

The benchmark EU carbon price fell by 0.44 euro to 28.82 euros a tonne.