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