* Theddlethorpe back in operation
* Met Office forecasts cooler temperatures
LONDON, July 22 British prompt gas prices fell on Monday as flows rose following a return to service by an import terminal, with much of the increased supply expected to be pumped into storage sites.
Gas for within-day delivery traded at 65 pence per therm, down 1 pence from Friday's settlement. Flows from UK gasfields gained as the Theddlethorpe terminal ramped up supply following the end of maintenance and an unplanned outage last week.
The day-ahead delivery contract rose 0.10 pence to 65.00 pence per therm.
ConocoPhillips' Theddlethorpe gas terminal was processing at a rate of around 10 million cubic metres of gas/day following the unplanned outage, while Norwegian flows were broadly steady.
Flows from Britain's gasfields rose to 105 mcm on Monday, up 4 mcm from Friday, although the amount of gas being pumped from liquefied natural gas terminals fell to 12 mcm from almost 16 mcm on Friday.
"Given the increased supply (from British gasfields), we could see net injections from medium-range storage sites today," said an analyst with Reuters Point Carbon.
Storage sites were 65 percent full by the end of Friday, up 1 percentage point from the previous day, according to data from Gas Infrastructure Europe.
The UK gas market was slightly oversupplied at 155 million cubic metres per day, compared with forecast demand of 154.2 mcm, National Grid data showed.
Britain's Met Office maintained its forecast that temperatures would drop towards 25 degrees Celsius later this week after what is expected to be the hottest day of the year on Monday.
Further along the curve, gas prices were largely flat, with benchmark winter 2013 gas trading at 72.75 pence per therm, up 0.05 pence from Friday.
Day-ahead baseload power traded at 49.45 pounds per megawatt-hour, up 0.45 pound on Friday's close.