Calculating potential lost revenue

I have a furnished holiday let in Spain. All relevant taxes and duties are up to date in Spain but I did not realise I should declare this income on my UK self assessment returns since the taxes were already paid. I now realise that this was incorrect so I am preparing a worldwide disclosure to rectify this accidental ‘failure to notify.’ Please can you explain how to work out penalties for failing to notify when a tax return has been filed on time and the tax has been paid on time but an oversight meant a section that should have been filled wasn’t. The HMRC calculation tool doesn’t seem to factor in this circumstance. Also please can you advise how potential lost revenue is calculated on income from an EEA furnished holiday let where all taxes and duties have been paid in the country of origin and a double tax agreement is in place to ensure that no further taxes are payable in the UK. Is there an alternative way of calculating penalties when the percentage of potential lost revenue is the basis of the calculation but no tax is due?

Hi,
You do not need to work out any penalties that might be charged.  HMRC will notify you of this.  
If you have declared and paid your taxes in Spain, then you will also need to complete a foreign income page and claim Foreign Tax Credit Relief to account for the Spanish taxes paid.  
If you have received correspondence from the Worldwide Disclosure Facility, there should be a phone number included for you to contact them with any queries you might have. 
Thankyou.  

Thank you very much,I shall contact them .

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