Sept 1 (Reuters) - London"s FTSE 100 ended higher on Wednesday, helped by gains in travel stocks and retailers, while data showed UK factory activity grew in August at the weakest rate for six months. The blue-chip FTSE 100 index (.FTSE) climbed 0.4% to have its best session in three weeks, with travel and leisure stocks (.FTNMX405010) and retailers (.FTNMX404010) both up over 1%. Meanwhile, a survey showed British factory output grew in August at the weakest rate for six months as supply chain problems weighed on manufacturers" recovery from the COVID-19 pandemic. read more The FTSE 100 has gained 10.6% so far this year, but continues to lag its European and U.S. peers as a resurgence in coronavirus cases across the world has sparked concerns of a slowdown in global economic growth. "Corporate results are strong, but the COVID crisis is not over," said Ipek Ozkardeskaya, a senior analyst at Swissquote Bank, adding the Delta coronavirus variant, global inflation spikes, and worsening chip and other material shortages would at some point affect businesses. "But the markets are on path for more gains. Nobody can tell how healthy the actual trend is, where it will end, or how it will end ... but for now, the overall market holds on to its gains and no one dares saying "the king is naked"." The domestically focussed mid-cap index (.FTMC) advanced 0.6%, hitting another intraday record high at 24,290.06. Homebuilders (.FTNMX402020) fell 0.1% despite figures from mortgage lender Nationwide showing British house prices rose by 2.1% month-on-month in August. read more Among stocks, WH Smith (SMWH.L) slipped 3.8% to be the worst performing stock on the mid-cap index after the retailer provided a grim annual profit forecast. read more JD Sports Fashion (JD.L) rose 3% after Berenberg raised its price target on the stock of Britain"s biggest sportswear retailer. Reporting by Devik Jain and Amal S in Bengaluru Editing by Subhranshu Sahu and Mark Potter Our Standards: The Thomson Reuters Trust Principles.