* LSE and easyJet storm into top British index
* Kazakhmys and Intu consigned to mid-caps
* Serco and Wood Group gain reprieve after earnings surge (Adds context, recent price moves)
By Alistair Smout
LONDON, March 6 (Reuters) - Low-cost airline easyJet and the London Stock Exchange will be promoted to Britain's top share index in the latest reshuffle, exchange operator FTSE said on Wednesday.
Both stocks have added over 40 percent since the last reshuffle of the FTSE 100, with easyJet buoyed by rising passenger traffic and LSE by a pick-up in trading volumes.
It will be easyJet's first time in the FTSE 100, while LSE will regain blue-chip status for the first time since June 2010.
They will replace shopping centre owner Intu Properties and miner Kazakhmys, which have been demoted to the mid-cap FTSE 250.
Both stocks had looked set to retain their blue-chip status earlier in the week, but became the smallest FTSE 100 stocks by market capitalisation after Serco and John Wood Group surged on Tuesday following expectation-beating results.
Serco gained 8.9 percent, with John Wood Group adding 7.9 percent, enough to retain their FTSE 100 positions. The index changes were calculated from prices at the close on Tuesday - had they been calculated from Monday's close, both companies would have been demoted.
All index changes are due to become effective from the start of trading on March 18, FTSE said.
Tour operator Thomas Cook will also to become a mid-cap stock, after gaining promotion from the small-caps index , along with online gambling firm 888, NMC Health and engineering firm Keller.
They will replace haulage company Stobart Group, JD Sports Fashion, property investment firm Raven Russia and British Assets Trust, who drop out of the FTSE 250 into the small-caps index. (Editing by Simon Jessop/Ruth Pitchford)