Withdrawing from AC IFISA, but keeping in (IF?)ISA wrapper

You can transfer from an IFISA to an IFISA elsewhere or another type of ISA completely. You need to get a transfer form from your new provider. You will enter your AC IFISA details on the transfer form and your new provider will do the rest for you. Your AC holdings need to be in cash for the move to occur (you can't take your loan-parts off the AC platform). It can take a little while for the transfer to complete, so allow 3-4 weeks at least.

I should also mention that you cannot split your current year's contributions to AC at the time you move (so you will need to move all or nothing - you can't keep half of the current year's contributions on AC and transfer the rest). However, if you have made contributions to your AC IFISA in previous tax years then you are allowed to split those funds however you wish at the time of transfer.

Neither Fidelity nor Vanguard would when I asked.
Of course they could accept it if they chose to, so seems odd that they don't want that pot of ISA money.

Hargreaves Lansdown accept partial or full transfers from IFISAs - I recently did one.  Vanguard will only accept transfers of the entire IFISA which is not really any use when you still have loans outstanding.  In order to transfer my IFISA to Vanguard I am currently in the process of doing a partial transfer to the Coventry Building Society followed by the complete transfer of that to Vanguard.  Oh the joys of filling in all the forms......

As it happens I've recently applied to transfer an IFISA to a S&S ISA. The application form made me choose between the incoming funds being a cash ISA or a S&S ISA. I selected the cash ISA option because that seems to essentially be what I'm looking to transfer - the excess cash that I have on the platform not the loans I'm invested in.

I'll report back on whether this has worked or if it gets rejected.

Won't be particularly happy if it turns out that you can put money into IFISAs but not move them out.

Although having said all that new tax years seem to come round quicker than I can find the available money to invest in new ISAs.

I suspect that's going to need the regulator to mandate 7 day transfers. If it can be done for current accounts, you'd think it was possible for ISAs.

Ah, yes, I too remember someone else reporting that funds swept into QAA from the cash account could be transferred out just fine. In "unusual market conditions" AC could decide to block all withdrawals from QAA and that could block your transfer (never happened to date).
The number I've supplied in the past for the AC account number is the reference number used for transfers into my IFISA cash account. To find this, click the Manage Funds button in the top-right corner and choose Deposit Funds -> IFISA -> Cash Account -> Reference.