UK GAS-Spot prices rise on high demand, lower Dutch supplies

* Gas system undersupplied by 20.2 mcm

* Demand 8 percent above seasonal norm

* Supplies from the Netherlands drop

LONDON, June 19 (Reuters) - British spot gas prices rose on Friday morning as lower flows from the Netherlands and higher-than-usual demand led to an undersupplied system.

Gas for within-day delivery fetched 43.45 pence per therm at 0825 GMT, up 0.95 pence on Thursday's close . Prices for day-ahead delivery were up 1 pence at 43.50 pence per therm.

With supplies at about 154.1 million cubic metres (mcm) per day and demand seen at 174.3 mcm, the system was 20.2 mcm undersupplied, National Grid (LSE: NG.L - news) data showed. Friday's demand was 8 percent above the seasonal norm of 162 mcm.

Traders said demand for gas from power generators was high due to an expected dip in output from the country's wind farms.

Wind generation was forecast at 2.9 gigawatts (GW) on Friday, falling to 1 GW on Saturday, compared with levels over 4 GW on Thursday.

Gas power plants provided almost 40 percent of the country's electricity supply on Friday morning.

Meanwhile, flows through the Netherlands' BBL pipeline dropped to near zero on Friday morning, National Grid data showed.

No one from BBL was available to comment immediately about whether the flow reduction was due to market reasons or a technical issue.

Gas prices further along the curve also rose, with the July contract up 0.22 pence at 42.55 pence per therm. Traders said the July contract firmed on the back of an extension of a Norwegian field outage.

Operator Gassco said on Thursday the field outage at 65 mcm a day would be extended into July.

In the Netherlands, the day-ahead gas price at the TTF hub rose by 0.2 euro to 20.60 euros per megawatt-hour.

In Europe's carbon market, the benchmark front-year price was trading at 7.45 euros a tonne on ICE Futures Europe, down 0.03 euro. (Reporting by Susanna Twidale; Editing by Dale Hudson)