They are likely to be replaced by investment firm Ashmore and equipment supplier Bunzl, pending a final decision later today by the FTSE EMEA Committee.
The firms moving up into the premier league of companies, calculated by market capitalisation, usually receive a boost as they are included in market tracking funds.
Conversely, fund managers who have invested in Wood Group and 3i could be forced to offload their stock in these companies.
Inmarsat and ITV were among the companies towards the foot of the table who avoided the big drop.
Just missing out on promotion were African Barrick Gold and Meggitt.
The near miss will be particularly painful for Meggitt director Peter Huber, who yesterday bought an extra £15,000 worth of shares in the firm, taking his total holding to just shy of £100,000 – inclusion into the FTSE 100 could have given him an instant return on his investment.