A full feasibility study was published in November 2021.https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1035650/a-fixed-link-between-great-britain-and-northern-ireland-technical-feasibility.pdf It estimated that a bridge would cost £335 billion, and a tunnel £209 billion. The study concluded that, although the technology exists to build either, any bridge would be “the longest span bridge built to date” and the tunnel would be “the longest undersea tunnel ever built”.
