Columbia Threadneedle is set to close three unit trusts after the firm said they had fallen below a size which was "economically unviable" to manage.
Effective 22 March, the firm said the £20.4m Threadneedle Navigator Growth Trust, run by senior portfolio manager Alex Lyle, and the £26m Threadneedle Navigator Income Trust, managed by the firm's head of investment grade, EMEA, Alasdair Ross, were unlikely to attract any future investments.
Furthermore, the firm knew of further planned redemptions on the income trust, which would reduce its size even more.
It noted the reason for closing the £36.7m Threadneedle Navigator UK Index Tracker Trust was because the firm had no plans to develop its range of index-tracking products.
The firm added it had considered other options to shutting the three unit trusts but found they were not in the best interests of investors.
Columbia Threadneedle are also transferring four more unit trusts from its Navigator range into its Managed suite, subject to unitholder vote on 14 February.
The Threadneedle Navigator Adventurous Managed Trust will merge into the Threadneedle Managed Equity fund, while the Navigator Balanced Managed Trust will become part of the Managed Equity and Bond fund.
The Navigator Cautious Managed Trust and Navigator Growth Managed Trust will merge into the Managed Bond Focused fund and the Managed Equity Focused fund, respectively.
A Columbia Threadneedle spokesperson said: "We are committed to providing our clients with the best investment opportunities and as such regularly review our fund range.
"In a recent review of our navigator range of unit trusts we identified some opportunities to merge strategies into existing funds in our range for the benefit of our investors.
"We also identified a number of unit trusts which we will close as they had fallen to a level which makes them economically unviable to run and unlikely to attract new investors in the future."