Boris Johnson's ambition for a bridge or tunnel between Scotland and Northern Ireland has been labelled as "very difficult and expensive" by a government-initiated study.

A review concluded the bridge would be "too technically challenging and expensive".

A government source has told the Sunday Telegraph that the PM's long-standing proposal will be formally ruled out in the coming weeks when a feasibility report from Sir Peter Hendy is published.

Sir Hendy, the Network Rail chairman, conducted a wider “Union connectivity review” to assess improvements to transport links between England, Scotland, Wales and Northern Ireland.

READ MORE: Boris Johnson backs away from 'world's most stupid tunnel'

A Government source told The Telegraph: “Hendy has examined if this is affordable and practical and he concludes it would be technically very challenging at the moment.

“That’s not to say it won't become viable at some point in the future, but at the moment it would be very, very difficult and expensive.”

The 28-mile tunnel from Portpatrick in Dumfries & Galloway to Larne in County Antrim, dubbed the ‘Boris burrow’, would cost £15bn to £20bn.

Both the Scottish and Northern Ireland governments questioned whether the money would be far better spent on something else.

In July, the PM’s former top aide Dominic Cummings was scathing about the idea. 

He said: “The Prime Minister’s only agenda is, buy more trains, buy more buses, have more bikes, and build the world’s most stupid tunnel to Ireland. That’s it.”