Boris Johnson’s pursuit of a bridge to Northern Ireland is a “waste of money” and a “vanity project” according to Scotland’s Transport Secretary.

Michael Matheson has written to Grant Schapps, the UK Transport Secretary, telling him the cash could be put to better use in other ways and to give it to the devolved governments in Scotland and Northern Ireland instead.

Mr Matheson raised the technical difficulties the bridge would need to overcome and has asked for talks on handing over the £20bn.

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The Prime Minister said he would be looking at feasibility study into building a bridge linking the south of Scotland to Northern Ireland with Portpatrick to Larne the likely route.

It would be 26 miles long and would have to negotiate a 160 metre deep trench in the North Channel and also a World War II munitions dump.

Mr Matheson said “I am concerned that pursuit of this in light of the already identified technical, logistical and safety challenges such as the Beaufort’s Dyke munitions dump could waste significant money and resource that could be put to better use on practical, deliverable projects.”

He added: “I strongly believe that if £20bn is available for investment in infrastructure in Scotland and Northern Ireland that rather than indulging the Prime Minister with this vanity project, such funding should be made available to our respective governments so it could be better spent on meeting the priorities of the people we represent.”