Sesame has been surpassed by long-time rival Bankhall in terms of number of RIs.
Durlacher says Bankhall passed Sesame last year, reaching 7,400 members if Point One, its non-regulated network, is included. This compares with Sesame's total of 6,400 if both its regulated and non-regulated businesses are included.
It says there is still a huge gap to the third-biggest IFA group with Tenet on 2,500 members.
Inter-Alliance is fourth with 1,100 RIs, followed by Bradford & Bingley with 1,000 RIs until it finds a buyer for its IFA subsidiaries, Aegon, including Positive Solutions, has a total of 950 RIs and Berkeley Berry Birch has 830 RIs.
Bankhall claims the group is even wider now that it has completed its purchases of Prudential's and Norwich Union's mortgage clubs.
The report says one of the reasons that RIs may have left Sesame is its levels of charges. It says its member fees stand at around 11 per cent, which, while down from historical levels of 14-16 per cent, are still considerably higher than Bankhall's at 4-6 per cent.