UK GAS-Prices lifted on supply downturn as maintenance limits flow

* Gas prices for next week up more than 5 percent

* Higher expected heating demand helps tighten system

June 1 (Reuters) - British gas prices jumped on Wednesday as demand rose and supply declined from liquefied natural gas terminals and elsewhere, as maintenance programmes constrained output.

The sharpest gain on any UK gas contract was for working days next week, rising 5.59 percent to 34 pence a therm by 0758 GMT, reflecting tight supplies.

UK gas markets were undersupplied by 25 million cubic metres/day, roughly 15 percent of current demand, according to data National Grid (LSE: NG.L - news) .

Gas for instant delivery rose 0.65 p/therm to 34.25 p/therm, while the day-ahead contract climbed 0.40 pence to 34.10 p/therm.

A confluence of factors including higher expected heating demand later this week, coupled with heavy maintenance, has made the transmission system less able to cope with disruptions, analysts at Thomson Reuters (Dusseldorf: TOC.DU - news) said.

Traders also blamed a drop in supply from LNG terminals on the first day of June.

"The start of June deliveries today has seen a marked drop off in LNG send-outs from South Hook (terminal), with current flows around 20mcm/d below recent averages at just 15 mcm/day," Marcel Boonaert, head of trading and portfolio at Wingas UK, said.

"Further planned maintenance outage also begins today, with works at both the SEGAL pipeline network and St Fergus terminal limiting flows from the UK Continental Shelf," Boonaert said.

At Britain's biggest gas storage site Rough, 16 mcm/day of gas is to be injected after the site returned from a week-long maintenance outage, further draining supply available on the market, Boonaert added.

Further along the curve, the contract for winter 2016 gas delivery fell by 0.15 pence to 37.20 pence/therm.

The Dutch day-ahead gas price at the TTF hub rose by 0.07 euro to 14.25 euros per megawatt hour.

In the European carbon market, front-year allowances eased by 0.11 euro to 5.99 euros a tonne. (Reporting by Oleg Vukmanovic in Milan; Editing by David Holmes)