Mobile and internet provider Carphone Warehouse is set to join the FTSE 100, the elite club of the UK's most valuable stock-market listed companies.
Carphone Warehouse was founded in 1989 by Charles Dunstone
The FTSE is reshuffled on a regular basis and its membership will be based on Tuesday's closing share prices.
Carphone Warehouse, now ranked 95th in terms of market value, should be joined by the newly-merged housebuilder Taylor Wimpey and oil firm Tullow Oil.
They are set to replace Kelda, power firm Drax and property firm Segro.
The results of the reshuffle are due to be officially announced on Thursday after a review meeting by the FTSE committee.
The changes should be implemented on 21 September.
Promotion to the FTSE 100 tends to boost a company's share price because many investment funds have to hold shares in all of the index's components.