The within-day contract was down 1.00 pence at 27.75 p/therm by 0845 GMT.
The day-ahead contract was down 1.40 pence at 27.25 p/therm.
"Temperatures are turning warmer and wind forecasts are also high over the week," a gas trader said.
Average temperatures in Britain are forecast at 5.1 degrees Celsius on Wednesday, rising to 8.1 degrees on Thursday, Eikon Refinitiv data showed.
The temperatures were up 1.2 degrees and 3.2 degrees, respectively,, on previous forecasts.
Peak wind power generation is forecast at 12.7 gigawatts (GW) on Wednesday, and 13.4 GW on Thursday, Elexon data showed.
"Our model forecasts gas for power consumption at 33 mcm/d (million cubic metres) for today and tomorrow. This is down from 40 mcm/d forecasted for yesterday," analysts at Refinitiv said in a daily research note.
Further out on the curve prices also slipped.
The February contract was down 0.63 p at 27.52 p/therm.
The Summer 2020 contract was down 0.26 p at 26.38 p/therm.
The day-ahead gas price at the Dutch TTF hub was down 0.40 euro at 10.48 euros per megawatt hour.
The benchmark Dec-20 EU carbon contract was down 0.12 euro at 24.54 euros per tonne.