I assume that as your wife was on PAYE, either the tax on her share of the rental income was being collected through her tax codibg or there was no rental profit.
Your wife or your accountant should have registered her for self-assessment using a form SA1
, regardless of the fact that she was on PAYE. Unless a tax return is completed to report a capital gain, the tax office will be none the wiser.
As you will see on page 2 of the SA1, a reason has to be given for registering for self-assessment. "I have Capital Gains Tax to pay" would have been your wife's reason. I am surprised that your accountant does not appear to have dealt with this and his apparent inaction has now left your wife open to a penalty for failure to notify HMRC of a tax liability and/or penalties for late payment of the CGT liability as well as late payment interest. You can read about failure to notify here
and about late payment penalties here
I realise this is not good news and you should either contact the tax office on the number here
to explain the situation or have your accountant do it for you. In order to stop interest charges accruing on the tax liability, you might consider to buying a certificate of tax deposit which you can read about here
. When such a deposit is used to pay tax, the payment date is the same as the certificate purchase date.
Let me know if you have any further questions.