The rally in global stocks has pushed several stocks back into the index
The London Stock Exchange (LSE) and private-equity firm 3i will rejoin the benchmark FTSE 100 index on 22 June.
Plumbing firm Wolseley will also return to the index of the UK's 100 largest companies by market value.
They will replace power firm Drax Group, leisure firm Whitbread and insurer Amlin.
FTSE reviews the index every quarter, with companies getting promoted based on certain criteria, such as becoming one of the 90 largest firms.
The final calculations were based on Tuesday's closing share prices.
Entrants to the FTSE 100 frequently see their share price benefit as funds that track the index are forced to buy them, while share prices of those that are relegated typically see a fall.
The LSE, the company which runs the London stock market, and 3i both benefited from renewed optimism that the worst of the financial crisis is over, which has pushed stocks worldwide higher.