One very cogent argument, amongst many, for interconnecting the United Kingdom by fixed link is the strong potential to develop Belfast further as a deep water port from an all-UK viewpoint as an addition to ports like Southampton.
This means expansion of productive industries as freight and logistics both in the port and beyond.
Belfast Port has the unique advantage of being on doorstep of the North Atlantic and the great circle route.
Directly diagonal is London – and continental Europe via Channel Tunnel via rail freight train.
This would of course necessitate a reinstatement of the Dumfries-Stranraer line in some shape or form, and that can only be good in itself.
John Barstow, Pulborough, West Sussex