The within-day contract was up 1.50 pence at 32.75 p/therm by 0925 GMT.
The day-ahead contract was up 1.50 pence at 32.50 p/therm.
Traders said cooler temperatures than previous forecasts had increased demand for gas, which combined with the weaker LNG supply to push prices higher.
The average temperature in Britain is expected at 5.4 degrees Celsius on Monday, falling to 3.7 degrees on Tuesday, Eikon Refinitiv data showed.
The temperatures were 0.4 degrees and 1.3 degrees lower respectively than the previous forecasts.
Britain's gas market was 29.5million cubic metres (mcm) undersupplied on Monday, with demand forecast at 318.7mcm and supply flows forecast at 289.2mcm, National Grid data showed.
Sendout from the country's LNG terminals was down 26 mcm compared with the previous day, Refinitv data showed.
LNG supply is expected to ramp up over the next few weeks, with around 19 tankers set to arrive before the end of the month.
Further out on the curve prices were little changed.
The January gas contract was flat at 0.20 p at 35.00 p/therm.
The summer 2020 contract was down 0.25 p at 32.00 p/therm.
The day-ahead gas price at the Dutch TTF hub was up 0.10 euro at 13.10 euros per megawatt hour.
The benchmark Dec-19 EU carbon contract was down 0.04 euro at 23.98 euros per tonne.