Downing Street has played down plans said to be backed by Boris Johnson for a bridge across the English Channel to boost relations with France.

Theresa May‘s spokesman gave a cool response to reports of the bridge, saying that he had “not seen any plans” for such an ambitious infrastructure project.

It comes after Mr Johnson, known for backing grandiose infrastructure schemes, asked whether the Channel Tunnel should only be the “first step” in terms of links with France.

The Number 10 spokesman said: “I haven’t seen any plans on that. But what I would say is...we are going to have very good economic ties with France economically, culturally, in areas such as defence and security for many, many decades to come.

“What was agreed yesterday, and what the Foreign Secretary tweeted about as well, is a panel of experts who will look at major projects together including infrastructure and we want to work very closely with our French colleagues on building a shared prosperous future.”

Pressed further on whether a bridge was an option, or whether the PM knew Mr Johnson might raise the prospect, the spokesman repeated that he had “not seen any plans”.

Emmanuel Macron and Theresa May arrive at Sandhurst

The Foreign Secretary raised the issue while at a summit between the British and French Governments at Sandhurst on Thursday, after tweeting out “our economic success depends on good infrastructure and good connections. Should the Channel Tunnel be just a first step?”

He is understood to want a new fixed link between the UK and France and believes “it’s crazy that two of the biggest economies in the world are connected by one railway line when they are only 20 miles apart.”

Sources close to Mr Johnson were reported to have said that the French President was enthusiastic about Mr Johnson’s suggestion of a bridge.

A joint declaration after the summit at the Royal Military Academy at Sandhurst, said: “The United Kingdom and France have a long history of collaboration in delivering cutting-edge technologies.

“Whether pioneering supersonic travel or better connecting our countries through the Channel Tunnel, cooperation between our nations has produced radical innovation.”