Apple

By “Apple account” do you mean the Apple Cash wallet? Because if so, they have an option to transfer money from there to a bank account.

Nope, it’s what used to be called iTunes money now.

Assuming you’re referring to Apple Store credit, I’ve run into this exact scenario before in a somewhat related way. Accidentally claimed a gift card I meant to send to someone else (be careful with that redeem button in the email lol, it’ll instantly apply the balance to your account with one click, so don’t fat finger it like me 🥲). Apple support wouldn’t (or couldn’t) undo that action. In other words, it’s a one way street. Once the credits enter your account, they can’t be used anywhere other than the Apple Store/icloud/App Store/etc

Apple's official policy is you can't access that money as cash "except as required by law".

In other words, if UK law says you are entitled to the money, then Apple would know that, and you simply need to contact Apple and ask them to give the money to you, as cash (or a bank transfer).

They don't like doing it, they want you to spend the money with them, but in many countries they are required to by law. Because it legally is your money - Apple classifies it as being spent when you use it to buy something, not when you add to your balance.

Depending how the money was deposited in your account, you might not get all of it back. For example target often sells $100 Gift Vouchers for $80. Try to get them to give you $100 cash in that situation, and there's a good chance Apple will only give you $80 (Target didn't make a loss of $20 on that gift card, and neither will Apple). But it doesn't sound like that will affect you.

PS: Transmit is awesome. Been a user for decades. The Mac App Store version is more expensive (subscription pricing with a lot of the money going to Apple) and has less features (some important features are not allowed in App Store apps) - so yeah, don't buy it from the App Store.