认真的观察者对英国总理鲍里斯·约翰逊（Boris Johnson）计划对苏格兰和北爱尔兰之间的固定联系的计划的可行性表示了极大的疑问，这将穿越巨大的，充满炸弹的深海谷。根据新的官方数字，确认这些疑问使政府损失了120万美元的研究。

在建立两个国家之间的第一个联系具有政治吸引力的同时，在这种敌对的环境中建立世界上最长的桥梁或隧道的身体困难始终被视为挑战。

Undaunted, Johnson in October 2020 ordered a review, done by leading engineers Douglas Oakervee and Gordon Masterton, with technical input by Jacobs U.K. Ltd. and COWI A.S. They confirmed early doubts before Christmas and the study cost was recently revealed

The major obstacle to the crossing is Beaufort’s Dyke, a subsea valley up to 3.5 km wide and 200-300 km deep running for 45 km roughly parallel to the coasts. A tunnel would be about 400 m below sea level under potentially dangerous 40 bar of water pressure. A bridge would need spans of an unprecedented 4 km.

Additionally, parts of the trench contain millions of tonnes of unexploded bombs and shells dumped from World War I until the 1970s.

Johnson's reviewers studied a corridor looping north of the dyke for a tunnel, in up to 200 m of water. Including the long approach ramps on either shore, the tunnel would be over 80 km long and cost $26 billion.

由于“技术不成熟”排除了一条浮动隧道，而长度和深度取消了一个沉没的管子选项，工程师则选择了机器驱动的，带有中央服务孔的双隧道。

For the roughly 30 km, multi-span suspension bridge option, the team chose a more direct route, crossing the dyke at its narrowest. It would cost $43 billion.

Including extensive approaches and other supporting infrastructure, the whole tunnel scheme would come in at up to $280 billion with $450 billion being the estimated cost of the bridge option. While technically feasible, the whole idea would be "impossible to justify," concluded the review, condemning the project for now.

The fixed link was the latest Johnson infrastructure ambition to flounder.

As mayor of London, he spent a reported $7 million to promote a major airport in the Thames Estuary, instead of the then proposed expansion of the city's Heathrow airport, which he opposed.

A specially convened government Airports Commission dismissed the estuary idea in 2014 on cost and environmental grounds. In 2016 the government approved a new, third runway at Heathrow.

一年后，约翰逊（Johnson）为泰晤士河（Thames River）的2.5亿美元花园桥计划被纽约市的新市长萨迪克·汗（Sadiq Khan）报废，此前已花费了超过7000万美元的设计和现场调查。

提升为一个私人资助项目,这笔交易set up by Johnson would have required the city to underwrite the cost of maintaining the 368 m long crossing in case the owner Garden Bridge Trust, failed to secure necessary financing, according to Khan.

In the end, the city and central government would have had to take on nearly all the up front cost of the supposedly privately financed, never-built, plant-laden structure.