* Within-day gas down 0.80 pence at 28.90 p/therm
* Gas system oversupplied by 19 mcm
LONDON, Feb 4 (Reuters) - British wholesale gas prices fell on Thursday morning due to ample supply and relatively mild temperatures.
Gas for immediate delivery had dropped 0.80 pence to 28.90 pence per therm by 0851 GMT from the previous settlement.
Gas for day-ahead delivery slid by 0.45 pence to 28.90 pence/therm.
Britain's gas system was oversupplied by 19.3 million cubic metres (mcm) on Thursday morning, with demand forecast at 286.3 mcm and flows at 305.6 mcm/day, National Grid (LSE: NG.L - news) data showed.
Domestic gas supplies from the UK Continental Shelf are strong at 145 mcm, while flows through the Langeled pipeline from Norway are ample at 60 mcm.
The oversupply is cushioning the impact of a series of outages at gas storage sites in Britain and the Netherlands on Thursday morning, traders said.
Gas consumption has declined from Wednesday as temperatures turned milder and are forecast to remain mild for the time of year until mid-February.
Long-term forecasts by the U.S (Other OTC: UBGXF - news) . International Research Institute for Climate and Society also point towards milder-than-average temperatures for the rest of this quarter, next quarter and in July.
In January, gas demand from the power sector was 0.58 billion cubic metres (bcm) or 51 percent higher year-on-year, according to consultancy Energy Aspects.
"Gas into power will be stronger (in the rest of the quarter), with the carbon price floor and lower expected gas prices pushing more gas into power," the analysts said.
"Over the current quarter, we expect gas into power will be higher y/y by 1.6 bcm," they added.
In the Netherlands, the day-ahead gas price at the TTF hub fell by 0.58 euro to 12.57 euros per megawatt-hour, while in the European carbon market, front-year EU allowances were down 0.05 euro at 5.59 euros a tonne. (Reporting by Nina Chestney; Editing by Dale Hudson)