Every now and again, fund management companies decide they do not want any more money invested in a particular fund and take the decision to 'close' it to new investments. This shouldn't be confused with a fund company deciding the fund should cease to exist – they simply don't want the fund to get any bigger.
Most of the time, fund companies will 'soft close' a fund. The definition of a soft-closure can vary, and it may just be that companies like Chelsea are asked to take the fund off their selection tables so that fewer people invest in the fund. However, in the majority of cases, it is when new investors cannot invest in the fund and a 'prohibitive' initial charge and/or a much higher minimum investment (a sum of money out of reach of most retail investors) is introduced to dissuade investors putting more money into the fund. The exception is usually monthly savings, which are allowed to continue without an initial charge, if they are already set up.
Occasionally a fund will be hard-closed. This is when no investments at all are taken and often, the fund is removed from fund platforms altogether.
Fund companies take these actions because they believe that if the fund gets any bigger, it will impact on the investment process and performance may be compromised. So these actions are taken to protect existing investors. The important thing to remember is that if you are already invested in the fund, there is no need to panic. The fund company is acting in your interests. Funds which are closed can be reopened at a later date..