UK gas prices slump 40 pct in 4 days amid heat wave, pipeline closure

* Major export pipeline closed

* LNG imports to add to glut

* High solar power output cuts demand

By Susanna Twidale

LONDON, June 15 (Reuters) - Prompt wholesale British gas prices have plummeted 40 percent since the start of the week and could fall further, as a heat wave cut demand and the closure of a major export pipeline left the market with nowhere to send excess gas.

Britain's within-day wholesale gas price, one of the most liquid prompt prices in the country's gas market, traded at 22.70 pence/therm at 1352 GMT, a 40 percent fall from last Friday’s close.

"The combination of warmer weather, plentiful supply and no route to export has left people holding gas they don't want and created a race to the bottom," said Nick Campbell, risk manager at Inspired Energy (LSE: INSE.L - news) .

Traders said the drop was caused by a series of factors, most notably the closure of the Interconnector UK (IUK) gas pipeline between Britain and Belgium for maintenance this week cutting off a key market for Britain's excess gas.

Demand has also plummeted as a heat wave has gripped the country.

Home heating usually accounts for around 40 percent of Britain's gas demand, while expected imports of liquefied natural gas (LNG) from Algeria and Qatar over the next few weeks have exacerbated the situation.

"Given the IUK shutdown, there is no real space to put this extra LNG," said Thomson Reuters (Dusseldorf: TOC.DU - news) gas analyst Oliver Sanderson.

Sanderson said that given the weak demand and plentiful supply, prices could keep falling but that he would not expect to see them trade consistently below 20 pence/therm.

Energy Aspects analyst Trevor Sikorski said the high temperatures also led to bumper output from Britain's solar power generators, cutting the demand for gas from gas-fired power stations to produce electricity.

Data from Britain's National Grid (LSE: NG.L - news) showed solar power was supplying around 20 percent of Britain's electricity on Thursday, while wind contributed a further 14 percent.

Traders said the market had been caught unawares by the LNG shipments. "The new catalyst was the LNG scheduled to arrive ... but it's everything," said a gas trader who did not want to be named as he is unauthorised to speak with the press.

Traditionally, excess gas is stored in the summer for use in the winter when demand is high.

However, Britain's largest gas storage site, Centrica (Frankfurt: A0DK6K - news) owned Rough, is unable to take injections of gas until next April due to concerns about the integrity of storage wells at the site. (Editing by Mark Heinrich)