The UK mining index <.FTNMX1770> surged more than 7 percent, bouncing back from a one-month low hit in the previous session. Before Wednesday's rally, the index had fallen about 16 percent since a 4-1/2 month high in March, pressured by a rising dollar.

Miners rallied following Yellen's comments that the U.S. central bank should proceed only cautiously as it looks to raise rates. That hit the dollar, boosting the value of dollar-earning firms that report profits in sterling.

Anglo American (>> Anglo American plc), Glencore (>> Glencore PLC), RIO Tinto (>> Rio Tinto plc) and BHP Billiton (>> BHP Billiton plc) jumped by between 6.3 and 12.5 percent.

"Global economic growth is spluttering and the idea that we'll see another rate hike from the Fed in the short term is being kicked into the long grass," Tony Cross, market analyst at Trustnet Direct, said in a note.

"This is also driving the dollar lower so commodity stocks are finding widespread support with the natural resource plays scattered across the top of the board."

The FTSE 100 index <.FTSE> was up 1.7 percent at 6,205.00 points in late afternoon trading and remained just a shade below its 2016 high of 6,242.32 points, touched in January.

Energy stocks were also in demand, with the UK oil and gas index <.FTNMX0530> rising 3.7 percent following a rally in crude oil prices. Shares in Royal Dutch Shell , BP (>> BP plc) and Tullow Oil (>> Tullow Oil plc) rose 3.3 to 4.3 percent.

Outside the blue chips, Premier Foods (>> Premier Foods Plc) was up 5.8 percent after U.S. firm McCormick raised its offer for the firm.

The new bid proposal of 65 pence per share was above the previous, rejected offer of 60 pence per share. Shares in Premier Foods traded at around 60 pence after the new bid was made.

"We see 65p as a good compromise price, allowing Premier's management to highlight the extra value it has extracted from McCormick, whilst also offering shareholders the opportunity of a cash exit today at a reasonably full ... valuation," analysts at Shore Capital said in a note.

(Additional reporting by Atul Prakash; Editing by Gareth Jones)

By Alistair Smout