LONDON, Sept 23 (Reuters) - British wholesale gas prices edged up on Monday in a slightly undersupplied market as an unplanned outage lingered and warnings of a strike in France raised the prospect of more gas demand in mainland Europe.
* The day-ahead contract rose 0.35 pence to 25.75 pence per therm as of 0755 GMT.
* The within-day contract had yet to trade but was bid at 25.02 p/therm, having closed at 23.60 p/therm.
* Britain’s gas system was undersupplied with demand forecast at 159.1 million cubic metres (mcm) and flows seen at 151.4 mcm, National Grid data showed.
* An unplanned outage at one of Britain’s largest gas fields, Culzean, continued on Monday, reducing flows by 11 mcm.
* Otherwise gas supplies into Britain were relatively stable with flows along the Langeled pipeline from Norway expected to come onstream on Tuesday.
* A union representing workers at state-owned French utility EDF called for a 24-hour strike starting on Monday at 1900 GMT due to government pension reforms.
* EDF nuclear power workers went on strike last week due to plans to restructure the company, pushing British and Dutch gas prices up due to higher demand after nuclear, hydro and gas power stations in France reduced output.
* “An undersupplied physical system and increasing gas for power demand for day ahead could push up (day-ahead prices) today,” Refinitiv gas analysts said in a note.
* “The delayed return of Culzean is an important factor in keeping the system undersupplied.”
* Peak wind power generation is forecast at 9.8 gigawatts (GW) compared to 12 GW of metered capacity and is expected to stay at such rates on Tuesday before falling off.
* The October contract was down 1.33 pence at 32.00 p/therm.
* The day-ahead gas price at the Dutch TTF hub fell 0.75 euro to 9.15 euros per megawatt hour.
* The benchmark Dec-19 EU carbon contract slipped 0.26 euro to 26.27 euros per tonne. (Reporting by Sabina Zawadzki; Editing by Dale Hudson)