The tunnel linking Wales and Ireland would be 'six times the length' of any other tunnel.

The tunnel, which would cost a whopping €251 billion, would be 'six times the length' of an other tunnel, however, building it hasn't come without difficulty.

Known as the Irish Mail Route, the tunnel would link Holyhead and Dublin and is just one of multiple proposed infrastructures to link the countries.

A €240 billion version of the scheme was rejected by the UK government in 2021, with the Financial Times reporting that it was 'dead, at least for now'.

A document further stated that chair of Network Rail, Sir Peter Hendy had 'agreed to add a seventh corridor … between Holyhead and Dublin', but hesitated due to the 'environmental and scale concerns' of the plans.

This doesn't mean plans for the tunnel are completely a miss though, as calls for a link between the countries date back to Victorian times!

Just five years ago, then Prime Minister, Boris Johnson, suggested a bridge between Scotland and Ireland.

As well as acknowledging its detractions, the 2021 report suggested a project such as the Irish Mail Route would create over 35,000 new jobs and deliver a major boost to the UK economy.

Currently, travelling between Ireland and Wales takes upwards of four hours, whereas the tunnel would be estimated to take about 30 minutes by car.

Despite having a hefty price tag and taking up to 30 years to build, the Irish Mail Route is also a frontrunner because of its cohesion with existing road and rail routes in both Dublin and Holyhead.

"Intuitively, Holyhead to Dublin is a more preferable route to the others,” former chairman of the British Tunnelling Society, Bill Grose told the BBC.

He added: "It’s closer to Manchester and Liverpool and connects straight to Dublin.”