Assuming that you are a British citizen and are asking for your spouse.
What visa does your spouse have in Italy? If s/he was issued
an Article 10 Residence Card on the basis of your British citizenship, she can use that to travel to the UK, provided s/he is either travelling with you or travelling to join you in the UK.
It does not however give him/her any residence rights in the UK. It substitutes for a visit visa.
Also, marriage to a British citizen does not give any automatic right to British citizenship/nationality. One must apply in the usual way, after at least five years residence in the UK and after acquiring either PR (under EU law) or ILR (under UK immigration law).
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.