For Italy, this is no problem for the ages 15 to 17 (inclusive)
For both (Italy and Switzerland) is is advised to get a written consent from the parents which should include your name and address being visited.
Theoretically this could also be asked for when leaving the United Kindom.
The link below contains a link to a Swiss form that should serve your purpose well since the field descriptions are listed in all needed languages.
All parents must sign it and a copy of a Photo ID (Driver’s Licence) should be included.
Sources:
Credit:stackoverflow.com‘
4 Mar, 2024
4 Mar, 2024
5 Mar, 2024
5 Mar, 2024