UK GAS-Losses extend on mounting supply overhang, mild weather

* Prices drop across the board

* Network oversupplied, demand weak

Dec 24 (Reuters) - British gas prices fell on Thursday in thin pre-Christmas holiday trading as supplies rose and mild weather forecasts kept a lid on heating demand.

Gas for day-ahead delivery was down 0.75 pence at 30.50 pence per therm (p/therm) by 0828 GMT.

The system was 13.8 million cubic metres (mcm) oversupplied, with demand forecast at 234.3 mcm, National Grid (LSE: NG.L - news) data showed.

Mild weather meant demand was well below the seasonal norm of around 264 mcm.

The Met Office forecast temperatures above seasonal norms for the coming days at around 11 to 13 degrees Celsius, and windy conditions.

Norwegian exports remained strong with flows via the Langeled pipeline to Britain at around 54 mcm per day, down slightly from around 58 mcm the previous day.

Weekend gas prices fell 0.25 p/therm to 30.05 p/therm, while the benchmark summer 2016 price traded at 30.70 p/therm, down 0.13 p/therm compared with Wednesday levels.

In the Netherlands, the day-ahead gas price at the TTF hub was 0.28 euros lower at 13.65 euros per megawatt hour on Thursday.

In Europe's carbon market, the benchmark EU Allowance (EUA) edged down 0.02 euros to 8.27 euros a tonne. (Reporting by Oleg Vukmanovic in Milan; Editing by Mark Potter)