* Q2 LfL sales up 1.9 pct ex fuel
* Q2 total sales up 4.3 pct (4.4 per cent ex fuel
* Expects challenging economic backdrop to persist
* Says positioned to perform well in Christmas period
LONDON, Oct 3 (Reuters) - J Sainsbury , Britain's third-biggest supermarket group, posted better than expected quarterly sales growth, boosted by strong take-up of its own label range and the roll out of its convenience stores.
Sainsbury, which trails industry leader Tesco and Wal-Mart's Asda by market share, said on Wednesday sales at stores open over a year, excluding fuel, rose 1.9 percent in the 16 weeks to Sept. 29, its fiscal second quarter.
That compares with analysts' average forecast of 1.4 percent, a rise of the same magnitude in the firm's first quarter, and represents a 31st consecutive quarter of underlying sales growth.
(Reporting by Neil Maidment; editing by James Davey)