UK GAS-Prompt prices ease on increased supply from Norway

* System under supplied by 15 mcm/day

* Slovakian gas deliveries to Ukraine drop

LONDON, May 1 (Reuters) - British prompt gas prices were lower on Friday as increased availability of flows in Norway and continental Europe were expected to mitigate tightness in the UK market.

Gas for within-day delivery was down 1.9 percent at 45.15 pence per therm.

National Grid (LSE: NG.L - news) data showed supply was forecast at 218 million cubic metres (mcm) on Friday, while demand was seen at 233 mcm, showing the system was under supplied by 15 mcm.

This shortfall was overshadowed by flows from Norway to Britain via the Langeled pipeline rising sharply, boosted by maintenance ending at Troll and increased availability of gas in continental Europe.

"Ukraine has suspended reverse flows from Slovakia in light of their latest agreement with Gazprom for cheaper gas supplies from Russia for the next three months," Wayne Bryan, analyst at consultancy Alfa Energy, said. "This has resulted in more supply being available to the northwest European markets."

"This additional gas availability, combined with the ramp up in flows from Langeled, will weigh on European gas prices."

Slovakian gas deliveries to Ukraine are forecast to drop by 40 percent on Friday, data published by Slovakia's gas grid operator Eustream showed.

Meteorologists forecast temperatures above normal levels in the coming days, which is likely to weaken demand for gas for heating.

Further along the curve, gas for delivery next month was down 1 percent at 41.85 pence per therm.

In the Netherlands, the day-ahead gas price at the TTF hub was down 1.1 percent at 20.52 euros per megawatt-hour.

The benchmark European Union carbon price was trading 1.4 percent higher at 7.53 euros a tonne on ICE Futures Europe. (Reporting by Sarah McFarlane; Editing by Jane Merriman)