Certificate of residence to prevent double taxation - ITALY / UK

Hello, I'm a self-employed freelance journalist in the UK. I wrote three articles for an Italian newspaper and they asked me for a certificate of residence to prove that I live and pay taxes in the UK right now and to avoid double taxation. I started filling in the form but I am not sure about some questions. 1. Question: "Amount of income received from fees or self employment?" - Can I consider all of the three articles together in the same application? Do I have to put the net or the gross amount of income? 2. Question: "Which article of the country's Double Taxation Agreement covers the income in this request?" - I assume it's the 12, can you confirm? The company asked me to specify "Royalties" as payment description. 3. Question: "Do the subject to tax provisions apply to this foreign income? (Some Double Taxation Agreements state that a UK resident is only entitled to foreign tax relief on certain types of income if it is subject to tax in the UK.) - I can't find any information about it, can you please advise? 4. Question: "Do you need a certificate for a specific period of time?" - - Not sure how to fill this one either. The company just asked me to prove that I live and pay taxes in the UK. Also, do I have to request a certificate of residence every time I work for a company outside the UK? Do I have to request it again if I'll write other articles for this company in the future? Thank you for your help. Alessandra

Hi Alessandra Vescio,
You can request cerificate of residence at How to apply for a certificate of residence to claim tax relief abroad.  
The UK / Italian treaty can be found at CONVENTION BETWEEN THE GOVERNMENT OF THE UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAN.  
Article 14 covers independent personal services, such as freelance journalism.
The subject to tax rules are not appropriate for article 14, with Italy and the UK.
You can request a certificate of residence from the current date or for a period in the past.  
You cannot specify a future date, as we cannot confirm what your residence position will be at any time in the future.
Thank you.