Yes, you are able to transfer funds from an existing ISA - including a Cash ISA - into an IFISA. However, there are some rules in place and important processes to follow when doing this.
Firstly, you should be aware that if you are transferring money invested in an ISA during the current tax year, you must transfer all of it. On the other hand, if you are transferring money invested in an ISA during a previous year, you can choose whether you transfer all or only part of it.