* Rough gas storage in outage until Aug. 3
* British EU referendum closely watched
* Dutch decision on Groningen expected on Friday
June 23 (Reuters) - British wholesale gas prices fell on Thursday morning due to an outage at Rough gas storage site which will reduce the amount of gas which can be injected into storage over the summer and as the country went to the polls in a referendum on EU membership.
Gas for immediate delivery fell by 0.40 pence to 33.50 pence per therm by 0941 GMT, while the day-ahead contract lost 0.95 pence to 33.75 pence/therm.
On Wednesday, operator Centrica Storage Limited announced that its Rough gas storage facility would shut down for 42 days (until Aug. 3) while additional tests on a well were carried out.
This means Britain might go into the winter with record low gas inventories because traders are not able to inject gas into storage until August.
Traders said injections into Rough have fallen to zero as expected and flows through the Langeled pipeline from Norway have also fallen, leaving the system just balanced.
Further along the curve, the contract for gas delivery next month, was at 33.50 pence/therm, 0.5 pence down, while the next-winter contract eased by 0.1 pence to 43.45 pence/therm.
Traders are also closely watching the results of a British referendum on Thursday on whether to stay in or leave the EU.
If the referendum's result is to remain in the EU, the pound will likely rise against the euro which would be bearish for British gas prices.
In the Netherlands, the day-ahead gas price at the TTF hub rose 0.08 euro/MWh or 0.53 percent at 15.13 euros/MWh.
The Dutch government is expected to decide on Friday on gas production levels at its Groningen field after October 1, currently capped at 27 billion cubic metres (bcm).
In the European carbon market, front-year EU allowances eased 0.09 euro to 5.60 euros a tonne.
(Reporting by Nerijus Adomaitis and Nina Chestney)