Compatibility summary
You will need a travel adapter in San Marino; plug types used there differ from United Kingdom.
Plug comparison
United Kingdom plug types: G
San Marino plug types: C F L
There is no common plug type between United Kingdom (G) and San Marino (C F L). You need a travel adapter.
Voltage comparison
United Kingdom: 230V, 50Hz
San Marino: 230V, 50Hz
Voltage difference is within a range many devices tolerate; check your appliance label.