Work is under way "by a range of government officials" to look at the idea of building a Scotland-Northern Ireland bridge, Number 10 has said.
Boris Johnson has described the bridge as a "very interesting idea", while Ireland's premier Leo Varadkar has said it was "worth examining".
Two routes have previously been floated - from Portpatrick to Larne or near Campbeltown to the Antrim coast.
The Portpatrick route would be more than 20 miles across the Irish Sea.
