The firm recorded higher gross sales than any of its rivals during the period, according to data compiled by research house Fundscape.
Hargreaves Lansdown followed Cofunds, in terms of total assets at £78.2bn. The firm added gross assets of £3.4bn in the second quarter of the year.
The platform provider displaying the fastest growth rate in percentage terms was Aegon, which added £2.1bn in the second quarter, an increase of 13.6 per cent. Aegon bought Cofunds in August 2016.
On an industry-wide level, platform sales were strong, despite uncertain market conditions for much of the period in question.
Total assets on the platforms examined by Fundscape were £539bn, an increase of £19bn, or 4 per cent.
Gross sales in the second quarter jumped to £34bn — up 13 per cent on the previous quarter, and 37 per cent on the same quarter of 2016, according to the report. Year-to-date gross sales stand at £63bn.
Net sales of £14.4bn represented a 6 per cent increase on the first quarter of the year and a 50 per cent increase on the same quarter of 2016. Year-to-date net sales stand at £28bn.
Apart from Hargreaves and Cofunds, platforms in the top five by net sales were there by dint of exceptionally strong self and pension sales, according to the report.
Bella Caridade-Ferreira, chief of Fundscape said the figures point to "another exceptional quarter for the platform industry", helped by strong Isa and pension business.
"With gross and net sales of £6.3bn and £3bn respectively, Isa business was the second best on platform industry records thanks to a combination of last-minute and early-bird investors taking advantage of their Isa allowances in April.
"Nonetheless, the real momentum came from pension flows. With the advent of pension freedoms, investors and their advisers are reorganising and consolidating pensions on one platform.
"As a result of high transfer values, defined benefit transfers into DB schemes are also a defining factor of the pension trend.”
Top 5 platforms by assets Q2 2017
|Hargreaves Lansdown (est)*||£78.2bn|
|Standard Life (inc Elevate)||£49.2bn|
Top 5 platforms by asset growth Q2 2017