The within-day contract was down 0.35 pence at 16.25 p/therm by 0926 GMT.
The day-ahead contract was up 0.25 p at 16.25 p/therm.
Traders said fundamentally the market remains week amid low demand and plentiful supply but the day-ahead price was lifted on expectations of stronger demand from power plants and lower output from wind farms.
Britain's gas system was oversupplied by 8.8 million cubic metres (mcm) with demand forecast at 195.9 mcm and flows at204.7 mcm/day, National Grid data showed.
Peak wind power generation is forecast at 14 gigawatts (GW) on Monday, falling to 7.6 GW on Tuesday, Elexon data showed.
"Gas for power day-ahead forecast is at 42 mcm/day up by 12mcm/d from previous forecast," analysts at Refinitiv said in a daily research note.
Further out on the curve prices were also mixed.
The May contract was up 0.38p at 16.40p/therm.
The June contract was down 0.40 p at 17.00 p/therm.
Traders said signals for curve prices were weak given a dip in oil prices.
Oil fell on Monday, after Saudi Arabia and Russia delayed a meeting to discuss output cuts that could help alleviate global oversupply as the coronavirus pandemic pummels demand.
The day-ahead gas price at the Dutch TTF hub was down 0.15 euro at 6.90 euros per megawatt hour.
The benchmark Dec-20 EU carbon contract was up 0.82 euro at 18.75 euros per tonne.