* FTSE 100 up 3.1 pct, biggest rise since Nov. 2011
* Cyclical banks, oils, miners see strong gains
* EasyJet firms; update shows passenger growth
By Tricia Wright
LONDON, July 4 (Reuters) - Britain's top share index posted its biggest gain for 20 months on Thursday, boosted by cyclical financial, oil and mining stocks after the Bank of England and the European Central Bank signalled extended periods of monetary stimulus.
Both central banks left interest rates unchanged, but gave unprecedented guidance about their policy direction, making clear there were no near-term prospects of interest rate rises.
Banks, oils and miners hoisted the FTSE 100 up 3.1 percent to 6,421.67 points.
That marked its highest close since June 4 and its biggest daily percentage gain since November 2011, though volumes were thinned by the Independence Day holiday in the United States, leaving the market more susceptible to sharp swings.
"There's no reason why these markets shouldn't rally back up to their May highs," said Mark Priest, trader at ETX Capital, said. The UK benchmark is some 7 percent from this level.
Cyclical shares tend to be the most sensitive to economic developments.
Among individual movers, low-cost carrier easyJet rose 3.6 percent after announcing a 1.9 percent increase in passenger numbers in June.
On the second-tier market housebuilders rose, with Taylor Wimpey, Galliford Try and Redrow saying they would meet or beat full-year expectations.
The FTSE 100 has this week traded in a near 250-point range, buffeted by unrest in Egypt and a resurfacing of debt concerns in Greece and Portugal as well as Thursday's central bank news.
"Because volume is low you're more exposed to the risk," Jeremy Lyon, associate at Old Park Lane Capital, said.
Lyon favours utility Centrica, oil majors Royal Dutch Shell and BP, and consumer goods firm Unilever. (Reporting by Tricia Wright; Editing by John Stonestreet)