(Reuters) - British plus-size fashion retailer N Brown Group Plc (>> N Brown Group plc) has shrugged off weakness in the sector, with growth in online sales lifting first-half revenue, sending its shares up by around a fifth.

European fashion retailers such as Next Plc (>> NEXT plc) and Hennes & Mauritz AB (>> H & M Hennes & Mauritz AB) last month blamed warmer-than-expected weather for below-forecast results.

N Brown, known for its SimplyBe, Jacamo and JD Williams brands, said online revenue rose 7.5 percent, with 70 percent of its online traffic coming from mobile devices.

"Online is the most profitable channel for us, with higher basket sizes and lower cost on both marketing and processing", Chief Executive Angela Spindler said on a media call.

First-half revenue rose 1 percent to 429.4 million pounds.

The company's shares were up 16.7 percent at 205.1 pence at 1231 GMT.

N Brown, whose brands target women aged 30 and above, and those of a larger frame, has reduced its range of household and electrical items to focus on fashion recent years, and is moving away from catalogues to online.

Rival Bonmarche Holding Plc (>> Bonmarche Holdings PLC), which serves the 50-plus women's clothing market, warned on profit last month, citing volatility in the sector.

"N Brown has demonstrated that even within the tough market, there are going to winners and losers, and N Brown has been a winner over the last 12 months or so," said Darren Shirley, an analyst at Shore Capital.

The Manchester-based company said adjusted pre-tax profit fell 19.8 percent to 31.6 million. It added that the Autumn/Winter season has started in line with its plans and that it is comfortable with current market expectations for the full year.

(Reporting by Sanjeeban Sarkar and Rahul B in Bengaluru; Editing by Sunil Nair and Louise Heavens)

By Rahul B