* Britannia gas field maintenance to begin on Aug. 2
* Day-ahead prices up 0.72 p/therm
LONDON, Aug 1 (Reuters) - British gas prices for prompt delivery edged higher on Monday morning as both planned and unplanned outages led to expectations of lower supply.
Gas for immediate delivery was up 0.20 pence at 34.50 pence per therm at 1025 GMT from the previous settlement, while gas for day-ahead delivery was up 0.72 pence to 35.25 p/therm.
Traders said prices had ticked up due to outages at Britian's gas terminals but said the market had been fairly illiquid since a glitch with the National Grid (LSE: NG.L - news) website left many participants unable to see supply and demand data earlier in the day.
"We expect UKCS (UK Continental shelf) domestic production to drop from 101 mcm/d (million cubic metres/day) to 85 mcm/d as St Fergus Mobil flows decrease following the Britannia maintenance and Bacton Seal deliveries could start dropping ahead of the maintenance starting on Wednesday," gas analysts at Thomson Reuters (Dusseldorf: TOC.DU - news) said in a daily research note.
Gas prices further along the curve also edged higher, with the 1Q 2017 gas contract up 0.05 pence at 45.70 p/therm.
In the Netherlands, the day-ahead price at the TTF hub rose 0.2 euro at 13.75 euros per megawatt-hour.
In Europe's carbon market, the front-year EU allowance price was down 0.03 euro at 4.40 euros per tonne. (Reporting By Susanna Twidale; editing by Nina Chestney)