London to Dublin by train doesn't really compete with going by plane on time. There are very few direct trains to Holyhead and they don't seem to match up with the ferries. How good could it be? The only direct train still stops a lot in Wales (below) and takes 3hrs 45m. Was there a direct fast train in the past that stopped less? How fast did it go? How fast would the lines allow?
London Euston 09:02
Stafford 10:24
Crewe 10:45
Chester 11:13
Prestatyn 11:38
Rhyl 11:44
Colwyn Bay 11:55
Llandudno Junction 12:03
Bangor (Gwynedd) 12:20
Holyhead 12:47
Then how much time do you need to change onto the ferry? The fastest ferry crossings takes 2hrs 15m on the Dublin Swift.
London Euston 09:02
Stafford 10:24
Crewe 10:45
Chester 11:13
Prestatyn 11:38
Rhyl 11:44
Colwyn Bay 11:55
Llandudno Junction 12:03
Bangor (Gwynedd) 12:20
Holyhead 12:47
Then how much time do you need to change onto the ferry? The fastest ferry crossings takes 2hrs 15m on the Dublin Swift.