Investors also pointed to Federal Reserve Chair Janet Yellen's comments on Thursday that revived talk of an interest-rate hike this year, which would put U.S. monetary policy back on the path to normality after years of near-zero rates.

"You’re seeing Janet Yellen’s comments last night being cheered by the markets as seeing quite a nice push higher ... giving investors the confidence to step back into the market and pick up stocks at bargain prices," said Jonathan Roy, advisory investment manager at Charles Hanover Investments.

The blue-chip FTSE 100 index <.FTSE> was up 2.5 percent at its close, its biggest one-day jump since Aug. 27, at 6,109.01 points after falling 1.2 percent in the previous session. The benchmark index is still down almost 7 percent so far this year.

Financial companies also gained, with Barclays (>> Barclays PLC) and HSBC Holdings (>> HSBC Holdings plc) up more than 3 percent and Royal Bank of Scotland Group (>> Royal Bank of Scotland Group plc) rising 2.7 percent.

The UK oil and gas index <.FTNMX0530> rose 2 percent, with BP (>> BP plc) up 3.2 percent and Royal Dutch Shell up 1.9 percent in the wake of data showing the U.S. economy grew more than previously estimated in the second quarter.

Mining companies, despite staging a rebound early on in the session, steadied in line with copper prices . The UK mining index <.FTNMX1770> was up 0.2 percent, although it is down almost 14 percent for the month.

"Given that the commodity stocks have been hammered so hard in the last couple of weeks, traders are very quick to latch on to any positive news. Copper and oil prices have made relatively small gains today, but mining and energy stocks have responded quite strongly," IG analyst David Madden said.

Autocatalyst maker Johnson Matthey (>> Johnson Matthey PLC) was up 5 percent, rebounding from Tuesday's heavy sell-off amid the scandal at German carmaker Volkswagen AG (>> Volkswagen AG), which said it had cheated in U.S. emissions diesel tests.

“There were some doomsday predictions earlier on in the week that the automobile sector and anything to do with it was done ... as we move into the weekend, these fears are being played down," said Roy, adding that investors were now picking the stock back up and buying some value.

Shares in mid-cap Synergy Health (>> Synergy Healthcare plc) leapt 42 percent after the company said the U.S. District Court for the Northern District of Ohio had ruled against the Federal Trade Commission's request for a move to block Steris from buying it out.

(Editing by Hugh Lawson)

By Kit Rees and Atul Prakash