Boris Johnson's £15bln Scotland-Ireland bridge branded bonkers by experts

Boris Johnson gestures as he delivers his speech at the Convention of the North, in the Magna Centre in Rotherham, norhtern England on September 13. Picture: Getty images

Engineering experts told the Guardian of the potential problems and spiralling costs concerning the prime minister's plan to construct a bridge between Scotland’s mainland and Northern Ireland.

Boris Johnson's plan to connect Scotland and Northern Ireland has been criticised by several engineers who have argued the idea of constructing the multi-billion pound bridge is "bonkers".

The comments come after documents leaked on Tuesday reported the Treasury and Department for Transport had been told to consider the possibility of building the bridge, after which the prime minister told schoolchildren the construction from Stranraer in Scotland to Larne in Northern Ireland would "only cost about £15 billion.”

Yet several engineers have warned that weather conditions between the two islands and unpredictable increases in costs would impede the possibility to complete the construction.

Engineer Chris Wise, who was part of the team behind London’s Millennium bridge, said it was “bonkers” to put a price on the plan before a proper design was in place. Another engineering academic labelled the proposal “dubious economics”.

The idea of the bridge was first hinted at last year, with two potential routes suggested: from Portpatrick to Larne or near Campbeltown to the Antrim coast.

During an interview, Mr Johnson said: “What we need to do is build a bridge between our islands. Why don’t we? Why don’t we?”

However, expert Mr Wise told the Guardian he has questions about the practicality of the project: “If Boris wants to stay prime minister he needs to stop promising figures before he can deliver them.”