UK GAS-Prompt prices plunge on oversupply, more LNG coming

* System oversupplied by 14 mcm/day

* Two new LNG cargoes heading to UK

Sept 1 (Reuters) - British wholesale gas prices plunged on Thursday on an oversupplied market, with more liquefied natural gas (LNG) cargoes heading to the country.

Gas for immediate delivery fell 2.75 pence or 12.1 percent to 20.00 pence per therm by 0850 GMT, while the day-ahead contract lost 2.2 pence or 9.6 percent to 20.80 pence/therm.

"Prompt prices have again opened the session lower, continuing the downwards trend seen through yesterday, with the news of additional LNG ... adding to direction," a UK-based trader said.

LNG supply from South Hook terminal has jumped by around 50 percent to 36 million cubic metres (mcm) per day to clear capacity for two cargoes due to arrive in the next seven days, he added.

Britain's gas system was oversupplied by around 14 mcm, with demand forecast to be around 189 mcm and supply at more than 203 mcm/day, National Grid (LSE: NG.L - news) data showed on Thursday morning.

Exports to continental Europe were nominated at full capacity of 57 mcm/day as the price difference between UK and Belgian gas hubs has turned negative and plummeted in recent days, analysts at Thomson Reuters (Dusseldorf: TOC.DU - news) said.

Prices further along the curve also opened lower, trailing prompt and coming under pressure from a fall in oil prices.

Gas for delivery in October fell 0.65 pence or 2 percent to 31.35 pence/therm, while the next-winter contract eased also by 0.65 pence to 38.90 pence/therm.

Oil prices fell 3 percent on Wednesday, after data showed a large weekly build in U.S (Other OTC: UBGXF - news) . crude and distillate stockpiles, but steadied on Thursday morning after Saudi Arabia said OPEC was moving towards a common position on oil production.

In the Netherlands, the day-ahead gas price at the TTF hub fell 0.45 euro or 3.8 percent to 11.30 euros/MWh.

European front-year carbon allowances were broadly unchanged at 4.46 euros a tonne. (Reporting by Nerijus Adomaitis; Editing by Dale Hudson)