UK GAS-Prices slide due to warm weather, oversupplied market

June 26 (Reuters) - British prompt prices fell on Tuesday as the country experiences a week-long heatwave that has reduced heating demand and left the market well supplied in the absence of sudden outages.

* Within-day contract was down 0.35 pence to 52.20 pence per therm (p/therm) at 0805 GMT.

* Day-ahead gas fell 0.2 pence to 52.25 p/therm.

* The whole country is expected to be dry and sunny, with higher than seasonal average temperatures forecast, reducing gas demand.

* The system was oversupplied by 12.8 million cubic metres (mcm), with demand seen at 148.6 mcm, below the seasonal average of 174.4 mcm, compared with supplies at 161.4 mcm, National Grid (LSE: NG.L - news) data showed.

* Supplies from the North Sea were steady on Tuesday at around 132 mcm and could climb by 4 mcm later in the day if production starts into the St Fergus gas terminal, which has undergone regular maintenance work.

* While Norwegian gas production has increased, the excess gas is being sent to the continent where gas prices are at a premium, so flows into Britain also remain stable.

* The IUK pipeline to Belgium remains under maintenance, trapping gas in the country, but is expected to start operations on Thursday.

* Average daily temperatures are seen at 18.6 degrees Celsius on Tuesday, dipping to 18.1 degrees C on Wednesday, Thomson Reuters (Dusseldorf: TOC.DU - news) Eikon data showed.

* In most of southern England and the Midlands, temperatures are expected to rise above 20 degrees C, with the themometre reading around 20 degrees C in Scotland, above average.

* The clement weather, however, has also reduced wind-power generation, which has fallen to 1 gigawatt (GW) on Tuesday from above 5 GW last week and compared with capacity of 12 GW, according to national grid data.

* The July contract was down 0.2 pence to 52.35 p/therm.

* Day-ahead gas at the Dutch TTF hub slipped 0.05 euro to 21.55 euros per megawatt-hour.

* The benchmark Dec (Shanghai: 600875.SS - news) -18 EU carbon contract was down 0.23 euros at 14.80 euros a tonne. (Reporting by Sabina Zawadzki; Editing by Mark Potter)