If you’re moving interest from a Cash ISA to a Stocks & Shares ISA, this doesn't count towards your annual ISA allowance as the money is already held within an ISA wrapper - so you can invest your interest even if you’ve contributed the full £20,000 for the tax year!
However, moving interest from a Simple Saver to a Stocks & Shares ISA does count towards your annual ISA allowance. If you’ve already reached your £20,000 limit, we’ll automatically pause your invest your interest payments until the new tax year begins and your allowance resets.