Citizens of some countries can come to the UK without a visa for up to 6 months for tourism, short study and business trips. It depends on what nationality is shown in the applicant’s travel passport!
For example: say you have Indian citizenship, but you live and work in Italy. Your Italian residence permit would not allow you to travel to the UK without a visa, seeing as Indian nationals are required to obtain a visa to travel to the UK.
Verify what nationality is shown in your passport!