He will continue running the European Smaller Companies Fund through a transition period under the supervision of Harry Nimmo.
The company is looking to fill the role but it is too early to give any more details, a spokesperson said.
Nicholson joined SLI in 2001 when he took over as investment director for smaller companies. He managed the European Smaller Companies Fund using bottom up stock picking as his investment style. Prior to this, he worked in sales and marketing roles at Aegon and Franklin Templeton.
The European Smaller Companies Fund is a pan-European fund, investing both in the UK and other continental European countries but domiciled in the UK and in denominated in sterling. Currently the fund has 24.2% in UK equities, with German equities making up a close second with 22.6% of the portfolio.
Following the announcement that Nicholson is leaving, Bestinvest suspended its rating of the fund, which it had previously given four stars.
“While Nicholson was the main driver behind the fund’s performance, he is supported by and part of a talented team, including the highly-regarded Harry Nimmo who is in a position to maintain the fund during the anticipated transition period. We will review the rating once a new full-time and dedicated manager has been appointed," Ben Seager-Scott, senior research analyst, said.
“In the meantime, this rating suspension shouldn’t be viewed as an outright indicator to sell, but investors may wish to hold off buying or adding until we have further information about the future of the fund," he aded.