The Department for Transport spent nearly £900,000 on research to see whether Boris Johnson’s dream of building a bridge or tunnel between Scotland and Northern Ireland could be realised.
The study, which cost £896,681, concluded a fixed link across the Irish sea could cost as much as £355bn and would be “impossible to justify”.
Led by Network Rail chair Sir Peter Hendy, the feasibility study was published in November but DfT made the cost of the research public only yesterday.
The idea for a fixed link was first floated by Johnson – then foreign secretary – in 2018, with sources quoting him as saying it “should be looked at more seriously”.
He later told the Sunday Times: "What we need to do is build a bridge between our islands. Why don't we? Why don't we?
"There is so much more we can do, and what grieves me about the current approach to Brexit is that we are just in danger of not believing in ourselves, not believing in Britain.”
Hendy concluded that while it would be technically possible to construct a bridge or tunnel link, the benefits “could not possibly outweigh the costs”.
A bridge would cost around £355bn, and a tunnel £209bn – far outstripping the prime minister’s estimate of “about £15bn”.
The project would also take nearly three decades to complete, it added.