Officials are examining the potential for a bridge linking Scotland and Northern Ireland, an idea championed by Boris Johnson.
Downing Street said a “range of officials” were looking at the idea, but were unable to say how many civil servants were examining proposals.
The Prime Minister’s official spokesman said it was a “proper piece of work” and Johnson was “ambitious” about infrastructure projects across the country.
Johnson has repeatedly spoken about the prospect of a bridge, even though experts have warned the depth of the Irish Sea and the presence of dumped munitions would cause problems for any project.
The project could cost a reported £20bn, although Johnson has previously said it would “only cost about £15bn”.
The Prime Minister’s official spokesman said: “The PM set out this was an idea which he believed could have some merit so, as a result of that, you would expect the Government to be looking into it.”
The scoping work is being run from Number 10, with a range of officials reporting into it.
“The PM is ambitious in terms of infrastructure projects,” Johnson’s spokesman said.
“He’s looking at a wide range of schemes across the UK which could improve connectivity.”
The Prime Minister told MPs “watch this space” when asked about the prospect of a “Boris bridge” in Parliament in December 2019.
The distance from Larne to Portpatrick, one of the most likely routes for a bridge, is around 45km.
There is no problem with distance, money or the Beaufort’s Dyke explosives disposal area, according to the Prime Minister.
In November 2018, he said: “The problem is not the undersea Beaufort’s Dyke or lack of funds. The problem is an absence of political will.”
Government sources said it was possible to build a bridge which has a tunnelled section to cope with some of the difficulties caused by the depth of the Irish Sea.
Follow STV News on WhatsApp
Scan the QR code on your mobile device for all the latest news from around the country