Hi
Under the circumstances you describe, your UK employer should continue to pay you through the PAYE payroll system when you relocate to Italy.
If, due to the length of your stay in Italy, you become tax resident there (and you are required to pay Italian tax on your employment income) you can apply for a code 'NT' by completing form P85.
If appropriate, HMRC would then authorise your employer to operate code NT until such times as you return to the UK.
PAYE operation: international employments
Get your Income Tax right if you're leaving the UK
Thankyou.