The day-ahead contract fell by 0.10 pence to 25.00 pence per therm by 0940 GMT.
The within-day contract fell by 0.15 pence to 25.15 p/therm.
Flows from Norway rose to 77 mcm on Monday from 70 mcm on Friday, Gassco data showed.
The rise was despite unplanned outages at Norway's Aasta Hansteen field and Kollsness plant impacting 25.8 mcm/day and 5 mcm/day, respectively.
Liquefied natural gas (LNG) send-out rose to 71 mcm on Monday from 51 mcm on Friday.
However, the gas system was almost balanced, with demand forecast at 255.1 million cubic metres (mcm) and supply at 254.7 mcm/day, National Grid data showed.
Demand was seen rising from levels observed on Friday and over the weekend.
However, overall, the weather was expected to remain mild, with a gas trader saying "there was no cold weather on the horizon" in Europe.
UK residential gas demand was forecast at 201 mcm on Monday and 223 mcm on Tuesday, Refinitiv data showed. This was lower than consumption levels at the beginning of the previous week.
Gas-for-power-demand is forecast to increase to 57 mcm on Tuesday from 40 mcm on Monday.
Peak wind generation is predicted to be robust, however, holding above 13 gigawatts (GW) out of 17.9 GW total metered capacity on both Monday and Tuesday, Elexon data showed.
The March contract was down 0.45 p at 23.65 p/therm.
In the Dutch gas market, the day-ahead was 0.25 euro lower at 9.60 per megawhatt hour (MWh) and the March contract fell to 9.60 euros/MWh.
The benchmark Dec-20 EU carbon contract fell by 0.59 to 23.29 euros a tonne.