A Totally Bonkers Proposal
 

See this: https://www.theguardian.com/uk-news/...rthern-ireland

It was also in yesterday's Sunday Times. The Guardian version does not mention the likely cost (before the inevitable cost over-runs!). Neither does it mention the millions of tons of high explosives dumped in the Beaufort Dyke.
Given that the Channel Tunnel went bankrupt, despite being technically much less of a challenge, never mind being very centrally located for traffic, how can anyone not laugh at such a risible proposal?

It comes up once a year. Engineering wise it is the simplest option but is the least commercial.

Dublin - Holyhead commercially is the best routing as you get Belfast-Dublin-Liverpool/Manchester/Birmingham/London in a direct routing

Engineering wise Dublin - Holyhead is a nightmare as it would be more than double the longest tunnel underwater currently

Brexit killed everything...