If you are transiting to the Republic of Ireland, you must pass through United Kingdom border in order to take a flight to Ireland. If you are a visa national or you qualify for exemption from the need to have a direct airside transit visa, you may transit without a visa providing you meet the conditions of the transit without visa concession and you have the correct documents for entry into Ireland.

If you are a national of a country to which the transit without visa concession does not apply and you are transiting to Ireland, you will need to hold a visit visa for the United Kingdom. A direct airside transit visa or visitor in transit visa cannot be used to travel to Ireland.