I've written before about options for travelling from London to Belfast without flying. Those options are all still available, but on my most recent journey last week, I discovered yet another one: overnight via Liverpool.
Route: Train to Liverpool, ferry to Belfast
Cost (single): £140* for a cabin (overnight)
Epicness: Very civilised. Bit of a faff getting from Liverpool Lime St to the ferry terminal (8 min Metro ride, 15-20 min walk; or you could get a taxi) but nothing major. Bit of a wait in Liverpool but plenty of food options.
Notes: You could also do this in the daytime but I'm not sure how well the trains work out, though the ferry part would be cheaper. The cabin was very comfy. This is now my favourite option.
* This was the cost for this trip per person: £65 London-Liverpool, £75 Liverpool-Belfast, with 2 people sharing a cabin. If you booked the train leg sooner, or were prepared to share a cabin or just have a seat, it would be cheaper. Daytime might also work out much cheaper.
For us, travelling with a baby, this was hands-down the best option. Leon slept happily all night tucked into the berth with me (and unlike the sleeper train, there was plenty of room for both of us). We only had one train journey with an awake needing-to-be-entertained baby; he fell asleep just after dinner in Liverpool and didn't wake up again properly (just roused briefly for feeds overnight) til Belfast.
This option is especially good now that the Belfast/Stranraer ferry is no more and you have to go via Cairnryan with a coach transfer; which sounds rather more faff to me than it used to be. Next time I think we'll do Liverpool/Belfast both ways.
We did do the Belfast/Cairnryan route on the way back as I was bound for Aberdeen, but unfortunately I still don't know how much faff it is. Due to flooding (coach delayed for unknown time), landslides (no train from Stranraer), and more flooding (couldn't get around flooding to Ayr), we wound up taking a 2 hr taxi ride to Dumfries instead, and a train down to Carlisle, before I headed north again. I do not recommend this as Happy Fun Times, although at least we're not still sitting in Cairnryan ferry terminal.