Estate executor I did not reassign bonds and incurred a chargeable gain. Can I appeal

I am the executor to my late father's estate and have made a stupid mistake. My father had two bonds which were subject to income tax. I did not realise that the bonds should have been reassigned to allow top slicing. I did not ask them them to be reassigned before encashment and they have now caused a sizeable tax liability on my tax for the financial year and for my sister, as benificiaries. Will HMRC allow an appeal to now reassign the bonds and allow top slicing?

Hi,
No, as this cannot be applied retrospectively.
Thank you.