Split income into accounts by proportion

I have a system with my business bank account whereby all incoming transactions automatically have 20% taken off of them and stored in a separate corporation tax account.

Is there any way to get Akaunting to do this too to keep the two aligned?

Unfortunately, that's not possible.

There may be a manual approach. You could create a transfer for each transaction or batch up by day/week/month and transfer the 20% to your tax account. At reconciliation you would need select the transfer transactions to match up to your bank statements.