Visit the website of the British government, it’s very easy understand what will be the documentation for your marriage
Marriage in Italy
Contact the local comune (town hall) before making any plans to find out about local marriage laws, including what documents you’ll need.
What you need to do
You’ll need to get a certificate of no impediment (CNI) from the authorities in the UK to prove you’re allowed to marry.
Your partner will need to follow the same process to get their ownCNI.
A CNI issued in England, Wales or Northern Ireland is valid for 6 months. A CNI issued in Scotland is valid for 3 months.
They’ll post your notice, and as long as nobody has registered an objection after a specified number of days (normally 15 or 21), they’ll issue your CNI.
Getting a statutory declaration
While you’re waiting for your CNI, you and your partner will need to make a statutory declaration before a solicitor or public notary. The Italian authorities will need this in addition to your CNI. There’s a standard template in English and Italian that you can download and use.
Legalisation and translation
You’ll need to get your statutory declaration and CNI ‘legalised’ (certified as genuine) by the Foreign & Commonwealth Office (FCO).
You’ll also need to get your CNI translated and sworn before the Italian courts or an Italian Justice of the Peace.
The names on all documents you provide must appear exactly as they do on your passports – if not, the authorities may refuse to allow the marriage to go ahead. You may need to provide evidence if the name on your passport is different to your birth certificate (eg marriage certificate or deed poll).
You can pay by cash or credit card, but not by personal cheque.