Online fashion retailer ASOS (>> ASOS plc) gained after saying its strategy of cutting prices in international markets was building momentum.
The blue-chip FTSE 100 <.FTSE> was up 0.5 percent at 6,806.24 points at 1346 GMT, after a 1.7 percent slide on Tuesday that trimmed its first quarter gains to 3.2 percent.
The index extended gains after data company Markit said its monthly manufacturing purchasing managers' index (PMI) rose to 54.4 in March from 54.0 the month before, the highest since July 2014.
"Encouraging UK PMI data, alongside positive economic news out of the euro zone, has helped the market. It’s supportive of the view that the economic recovery in the United Kingdom continues,” Robert Parkes, equity strategist at HSBC Global Research, said.
Another survey showed manufacturing activity in the euro zone accelerated faster than thought last month.
Among sharp movers, ASOS rose 4.1 percent after saying it was confident of hitting profit expectations for its 2014/15 financial year. Although ASOS posted a 10 percent fall in first-half profit, it exceeded forecasts.
"The online fashion retailer has implemented 'zonal pricing' which is slowly increasing international sales," Augustin Eden, analyst at Accendo Markets, said.
"(Labour leader) Ed Miliband has declared war on zero-hours contracts which are part of what keeps costs so low for firms like ASOS. Massive investment in its international operations will be an effective hedge against a less than satisfactory election result," he said, referring to a contract under which an employer is not obliged to offer any minimum working hours.
Over 100 British company bosses publicly backed Prime Minister David Cameron's Conservative-led government on Wednesday and warned a change of course for Britain's $2.8 trillion economy under a Labour government after a May 7 election would put economic recovery at risk.
Among sectoral gainers, the UK oil and gas index <.FTNMX0530> advanced 1.7 percent, tracking a rally in Brent crude oil prices as talks over Iran's nuclear programme continued, curbing expectations of an immediate deal that would allow Iranian crude onto the market.
The banking index <.FTNMX8350>, which fell 1.7 percent Tuesday, rose 1 percent on expectations an economic recovery will help cyclicals such as banks. Barclays (>> Barclays PLC) rose 2.5 percent, while Lloyds (>> Lloyds Banking Group PLC) gained 1.7 percent.
(Additional reporting by Francesco Canepa; Editing by Alison Williams and Susan Fenton)
By Atul Prakash