Both stocks have lost more than 40 percent in a torrid year so far for the broader Russian mining group, which includes ENRC <.ENRC.L>, beset by slowing demand, corruption probes and regulatory inquiries that have hit investor sentiment.

Evraz (>> EVRAZ plc), Russia's biggest steel producer which is also included in the mining sub-index <.SXPP>, and Polymetal (>> Polymetal International PLC) were the 149th and 118th biggest companies respectively on the London stock exchange by market capitalisation as of June 7. They are likely to follow copper miner Kazakhmys (>> Kazakhmys plc), demoted to the FTSE 250 <.FTMC> in March, when the reshuffle is announced on Wednesday.

If ENRC (>> Eurasian Natural Resources Corporation), the subject of a potential buyout, is eventually taken into private ownership that would leave no Russian mining stocks in London's blue-chip index.

Any company falling to 111th position or below is automatically deleted from the FTSE 100. Any company rising to 90th position or above is automatically added to the FTSE 100, according to FTSE rules.

Traded volumes and volatility in the stocks likely to move can jump in the days around the reshuffle as pension funds, exchange-traded funds and investment trusts with FTSE 100 tracker products re-weight their portfolios.

In terms of their market cap based on June 7 prices, Britain's biggest supplier of building materials, Travis Perkins (>> Travis Perkins plc), and housebuilder Persimmon (>> Persimmon plc), the 90th and 92nd largest listed UK companies, respectively, are the most likely replacements for the Russian miners.

Also in contention for promotion to the FTSE 100 are private equity group 3i (>> 3i Group plc) and shopping centre owner Intu Properties , looking for a swift return to the UK's blue chip index after being demoted in March's rejig, car insurer Direct Line (>> Direct Line Insurance Group PLC) and systems testing firm Invensys (>> Invensys plc).

Candidates for demotion to the FTSE 250 <.FTMC> also include oil services firms AMEC (>> AMEC plc) in 111th place and John Wood (>> John Wood Group PLC) in 110th place plus outsourcer Serco (>> Serco Group plc) in 112th place, according to data from Starmine.

Another Russian miner, Petropavlovsk (>> Petropavlovsk PLC), also faces possible demotion, to the FTSE Small Cap index <.FTSC> from the FTSE 250 along with asset manager Dexion Absolute Sterling (>> Dexion Absolute Ltd), customer management solutions provider SDL (>> SDL plc) and explorer New World Resources (>> New World Resources PLC).

Companies that could be elevated to the mid-cap index include business support services group DCC (>> DCC plc), insurer Esure (>> Esure Group PLC), estate agency Countrywide (>> Countrywide plc) and housebuilder Crest Nicholson (>> Crest Nicholson Holdings PLC).

(Editing by Susan Fenton)

By David Brett