I am Lebanese Citizen and am planning a trip to Ireland this month. A valid Irish visa is already in hand and I am willing to reach there through the UK.
Will I need a transit visa in the UK for few hours for flight connections to Ireland?
If you are stay in the airport for few hours and not cross the board, you need to have a Direct Airside Transit Visa.
This service will help you to understand whether or not do you need a visa in the UK
If you visit Northern Ireland you will need to get a UK general visit visa