UK GAS-Prompt prices flat, pressured by weaker demand

* Day-ahead flat at 43.60 p/therm

* Within-day down by 0.15 p at 43.60 p/therm

LONDON, July 7 (Reuters) - British prompt gas prices were little changed on Tuesday due to a slightly undersupplied system, and weaker demand from plant operators.

Gas for delivery on Wednesday was steady at 43.60 pence per therm at 0829 GMT, while gas for immediate delivery was 0.15 pence lower at 43.60 p/therm.

National Grid (LSE: NG.L - news) data showed demand was forecast at around 176 million cubic metres (mcm) and supply at 168 mcm/day.

Supply from Norway was mostly being diverted to the Continent and withdrawals from storage had increased from Tuesday.

Peak wind generation was forecast to rise on Wednesday to 4,797 megawatts from 4,307 MW on Tuesday, reducing demand from gas plant operators, which may be pressuring the within-day price, traders said.

In June, demand for gas from the power sector fell for the second straight month and was 23 percent lower on the year, largely due to higher renewable generation, a slight decline in coal-fired output and lower total power demand, said analysts at Energy Aspects.

Gas prices for winter 2015 delivery touched a record low of 47.00 pence per therm. The contract has been steadily falling for a couple of weeks.

Energy Aspects said the third quarter should have better pipeline supply from both Norway and the UK Continental Shelf, although Dutch supply will remain reduced due to a cap on Groningen field output.

Higher supply will mean more injections into storage, perhaps as high as 1.4 billion cubic metres which is almost double the injection level of the third quarter last year.

Dutch day-ahead gas at the TTF hub was down 0.08 euros at 20.92 euros per megawatt-hour.

"If Russia and Ukraine are unable to agree on a gas price for Q3 volumes, it would be bullish for European hubs as it would increase the risk of supply disruption and lead to higher reverse flows from Slovakia to Ukraine," said Thomson Reuters Point Carbon analyst Francois Flament.

Europe's benchmark carbon price was 0.04 euros lower at 7.35 euros per tonne on ICE Futures Europe. (Reporting by Nina Chestney, editing by Louise Heavens)