Mark Lyttleton, managing director on the UK equity team, which manages over 21 billion pounds, will leave the firm at the end of April, BlackRock said on Monday.
Nick Little, currently a director on the UK equity team, will take control of Lyttleton's UK Dynamic fund which will be merged into the BlackRock UK fund.
Nigel Ridge, a managing director at the firm, will manage the UK Absolute Alpha fund with existing co-manager Nick Osborne.
"Nick Little, Nigel Ridge and Nick Osborne are key members of the BlackRock UK Equity team, which is one of the largest in London ... and are able to draw upon the strength and depth of the broader team," BlackRock said.
According to Lipper, a Thomson Reuters company that tracks the fund industry, Lyttleton's UK Dynamic and UK Absolute Alpha funds have seen combined net outflows of about 900 million pounds over the 12 months to the end of February.
Returns over the year have also underperformed - 3.3 percentage points below the peer group average for the Absolute Alpha fund, and 8.7 percentage points for the UK Dynamic product according to Lipper data.
Lyttleton, who took a three month leave of absence in 2012, traces his career at the firm back more than 20 years. He joined Mercury Asset Management in 1992, later acquired by Merrill Lynch which in turn merged its fund unit with BlackRock in 2006.
(Reporting by Chris Vellacott; Editing by Mark Potter)