Great Western Coffee Shop

I need to get from bristol (we will assume bristol as not sure where I'll be working at the time) on friday 1st July returning sunday 3rd.

Parameters:  (1) I need to be in work on the thursday but can leave by 5pm (2) I don't mind overnighting on a ferry or train (3) I want to use train each side of the ferry (4) I need to be back in work for Monday morning but again don't mind overnighting in transit (4) I don't care whether I go from fishguard and up, liverpool/holyhead into dublin, or into belfast from liverpool/stranrear and down

People on here are much more knowledgable about planning these things than I am

Don't have the time to look through all those options right now, but have a look on the "SailRail" website - give it your English origin, Irish destination, dates/times and preferred sea route and it'll figure things out for you:

http://www.sailrail.co.uk/ (http://www.sailrail.co.uk/)

If you play your cards right there are some great deals around. Not sure if the 12-week advance booking window applies to these journeys or not though.

Edited to add

You're probably best off trying to do as much of the rail journey as possible this side of the Irish Sea. Getting round Ireland by train is generally a bit of an arseache, especially since since IE services to Rosslare are dire at best, with connections designed to miss arriving ferries by 5 minutes plus a fairly stiff walk to get to the station. So on that basis I'd recommend Holyhead to Dublin or Dun Laoghaire for the ferry sector.

Putting in the destination as "Dublin City" returns a fare of GBP 63.00 return on your chosen dates (standard class), using the Holyhead ferry.

You can also use the NRES journey planner to plan a journye to Dublin via Holyhead. Can't remember if it's Heuston or Connolly that's the relevant Dublin terminus but they're not very far apart. Scratch that, just choose Dublin Port, it's fairly central.

Pearse, Tara Street or Connolly stations, if you end up coming on the Dart train from Dun Laoghaire. Depends which side of the Liffey you want to end up. Pearse and Tara Street are south, close to Trinity College, Connolly is just north of the river.

Yes - I would suggest Holyhead; take a look at http://www.seat61.com/Ireland.htm  Shortest journeys, reasonable selection through the day, fares that are reasonable and can be booked on the day.

Sadly, the Birkenhead -> Dublin boat has now gone (I was at its former berth last night) and unless things have changed, the Bootle -> Dublin boat does not take foot passengers. Rosslare, as has been commented, seems designed to fail to connect and Stranraer is a l-o-n-g way round!

Central? I think not - it's a bus or taxi ride into the city centre. There's a shuttle bus that'll meet incoming ferries. Slightly more difficult to find the shuttle bus (Busaras? aka the coach station, near the Custom House) to take you out to Dublin Port, so I've usually ended up doing a taxi.

Dun Laoghaire is further away, but connected to the city by the frequent DART trains.

If you end up choosing a schedule including Stena rather than Irish Ferries, you might like to book via their own website.
It seems to work well, has a few more options for onboard the ship and when I used it on the other SailRail route (via Harwich) it ended up producing some very interesting rail tickets. Essentially the rail journey tickets for either side of the water were issued on Stena Line boarding card stock.
Certainly some of the more unusual tickets in the collection I've made over the years from the journeys I make.

Probably not viable but what about Heysham?

Just for the track bash!

I believe the ferry from Heysham goes to the Isle of Man. Another ferry service runs from IoM to Ireland, but I bet they don't connect!

The only sailings long enough for overnight berths are those from !
Liverpool, which either don't run now or don't take foot passengers, or those from Brittany to Ireland! Could be an interesting trip .. Nailsea to Plymouth, ferry to Brittany and then ferry back across to Cork or Rosslare. Take plenty of strong brown paper bags!!