UK GAS-Prices dip on ample supply, weaker oil

* System long 25 mcm - National Grid (LSE: NG.L - news)

* Oil falls below $33 a barrel

Jan 7 (Reuters) - British gas prices fell on Thursday as an oversupplied system and falling oil prices weighed.

Gas for immediate delivery traded down 0.85 pence or 2.5 percent at 33.75 pence per therm as at 1023 GMT, while the day-ahead contract was down 0.55 pence at 34.05 pence per therm.

Britain's gas system was oversupplied by 25 million cubic metres (mcm), with demand forecast at 278 mcm and supply at 303 mcm, according to National Grid data.

"The length on the system is putting pressure on the day-ahead contract, though with the cold snap still hanging over the coming weeks, support remains on contracts over the balance of January," said Marcel Boonaert, head of gas trading at Wingas UK.

Temperatures are forecast to fall below seasonal norms in the coming week, driving up demand for gas for heating and helping limit losses on some contracts.

Further along the curve, gas for February was trading down 0.27 pence or 0.8 percent at 34.38 pence per therm, as falling oil prices put downward pressure on gas contracts.

Oil slid below $33 a barrel on Thursday to levels not seen in more than a decade, as tumbling Chinese equities rattled investors already concerned by near-record production and massive stockpiles of unwanted crude.

In the Netherlands, the day-ahead gas price at the TTF hub fell 0.28 euros to 14.90 euros per megawatt-hour, while in the European carbon market, front-year allowances eased 0.03 euros to 7.78 euros a tonne. (Reporting by Sarah McFarlane; Editing by David Evans)