Ireland and UK Border Control

[Palantir]

Does anyone know if Ireland (ROI) and the UK share immigration information? Say someone travels from Northern Ireland to the mainland UK? Thanks.

[CR001]

Yes, they share immigration information.

Northern Ireland is part of the UK though.

[avta]

Does anyone know if Ireland (ROI) and the UK share immigration information? Say someone travels from Northern Ireland to the mainland UK? Thanks.

The information on the routes inside the UK such as (NI-Scotland) is not automatically uploaded to the Home Office entry/exit system. These are the internal UK routes.
As an example, the automatic UK visa overstay script will decide that you overstayed in the GB if you leave the UK true the land border to the ROI.
They will send you a message with the request to prove when and how you actually left the UK.