UK GAS-Norwegian shortfalls trigger rally, limit storage injection

* Norwegian flows drop sharply

* Day-ahead gas prices jump 1.4 pence/therm

Aug 26 (Reuters) - Prompt natural gas prices in Britain rallied on Wednesday thanks to supply shortfalls and driven by lower Norwegian deliveries, triggering reduced injection rates into storage sites.

Prices for Thursday delivery had jumped 1.40 pence/therm to 38.70 p/therm by 0758 GMT on the supply tightness, further exacerbated by reduced flows into Shell (LSE: RDSB.L - news) 's Bacton terminal.

Flows there dropped to around 7 million cubic metres (mcm) per day from 11 mcm overnight. Gas prices for the rest of the week climbed 1.45 p/therm to 38.75 p/therm.

Trending up with other contracts, gas for immediate delivery rose 1.55 p/therm to 38.80 p/therm.

Britain's gas network was undersupplied by 13.3 mcm, with demand estimated at 209.2 mcm, according to National Grid (LSE: NG.L - news) data.

Exports through the Britain-Belgium Interconnector steadied at 54 mcm/day due to the unchanged price spread between the two markets compared with the previous session.

Another potentially bullish factor came from Centrica (LSE: CNA.L - news) 's decision to delay a reduction in injection capability at Rough, Britain's largest gas reservoir. It (Other OTC: ITGL - news) has postponed a planned switch from dual-train to single-train injection at Rough to Aug. 25-28, without giving more details.

A switch to single-train injection would mean less gas being injected into Rough, resulting in more supply available on the market. But regardless of the delay, rising prices curbed injection rates on Wednesday.

Forecast injections into storage fell to 27 mcm for the current session from 38 mcm on Tuesday, analysts at Thomson Reuters Point Carbon said.

The main upset on Wednesday, however, was the sharp cut in Norwegian deliveries, with flows through the Langeled pipeline to Britain down 20 mcm day-on-day at 34 mcm.

The reason for the reduction was not apparent, with Norwegian grid operator Gassco not announcing any maintenance plans.

Further along the curve, gas for September delivery was up 0.75 pence at 39.40 p/therm.

Prices were also higher on the Dutch TTF market, with gas for day-ahead delivery up 0.07 euro at 18.95 euros per megawatt-hour.

In Europe's carbon market, benchmark EU Allowances (EUA) were 0.07 euro higher at 8.33 euros a tonne. (Reporting by Oleg Vukmanovic in Milan; Editing by Dale Hudson)