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I (Indian) have a travel itinerary from Dublin to India via UK Heathrow airport. From the airline website, it says that I need to move from Terminal 2 to Terminal 3 of Heathrow airport. As I have never been to Heathrow before, do I need to pass the border check/immigration? If so then do I need to have UK transit visa or some sort? I'm a work visa holder in Ireland. Please help me with this guys. Thanks!