Nearly £900,000 of taxpayers' money was spent on a study commissioned by Boris Johnson which found it would be too expensive to build a bridge or tunnel between Scotland and Northern Ireland.
The Department for Transport (DfT) said the research into the feasibility of a fixed link cost £896,681.
Network Rail chairman Sir Peter Hendy led the investigation, which found that a bridge would cost £335 billion, while a tunnel would require a budget of around £209 billion.
