Housebuilder Persimmon and Kazakhstan miner Kazakhmys are set to join the UK's FTSE 100 share index later this month, following the latest reshuffle.
Persimmon is buying rival Westbury
Bookmaker William Hill and Whitbread are likely be relegated from the main index. The changes are scheduled for the end of trading on 16 December.
The FTSE 100 is reviewed four times a year to ensure it represents the 100 largest UK listed companies.
Copper mining specialist Kazakhmys listed in London only in October.
It is the world's 10th largest copper miner.
Persimmon, the UK's biggest homebuilder, is in the process of buying rival Westbury for £643m.
Outside of the quarterly reshuffle, ports and ferry firm P&O is also rejoining the FTSE 100 in place of plasterboard company BPB which is being deleted after its takeover by French firm Saint-Gobain.
Last week P&O accepted a £3.3bn ($5.7bn) takeover offer from the United Arab Emirates firm Dubai Ports World.
If the takeover goes ahead, P&O will then leave the FTSE indexes.