I have really messed up the current bank account due to erroneous reconciliation. Can I start a new current account in the new finance year and keep the old one?

Yes, Angelika. You can start a new account at the start of the latest financial year to facilitate the reconciliation of transactions in QuickBooks Online (QBO) while keeping the old reconciliation. I'll provide more details and other methods to assist you with the reconciliation process.
 
Once you've added the new account, you'll want to manually import transactions so you can reconcile it. These are the steps:
 

1. Go to Transactions and select Bank transactions.
2. Select the blue tile for the account you want to upload the transactions into.
3. Click the Link account ▼ dropdown, then select Upload from file. If your account is not connected yet to online banking, select Upload transactions.
4. Select Drag and drop or select files and select the file you downloaded from your bank. Then, select Continue.
5. In the Select a QuickBooks account for the bank file you want to upload ▼ dropdown, select the account you want to upload the transactions into. Then, select Continue.
6. Follow the onscreen steps to match the columns on the file with the correct fields in QuickBooks. Then select Continue.
7. Select the transactions you would like to import. Then select Continue.
8. Click Yes to confirm and select Done.
    
   For visual reference, see the screenshot below.
    

I recommend checking the For customers using QuickBooks Online section in this article for more information about the process: Manually upload transactions into QuickBooks.
 
Another approach to fixing a reconciliation without opening a new account is to collaborate with an accountant. They have access to a specific feature in QBO that allows them to undo an entire reconciliation, helping you start afresh while keeping your books organized. For more information, please visit this article: Undo or remove transactions from reconciliations in QuickBooks Online.
 
On top of that, you can check this page to help you view or print reconciliation report from QBO: View, print, or export a reconciliation report in QuickBooks Online.
 
Our team encourages you to ask more questions via the comment section below. This way, we can extend a helping hand to address your concerns. For clarifications or assistance in dealing with reconciliation, let us know below. We'll get back to you as soon as possible.