We are contemplating flying to London, renting a car, wending our way through the Cotswolds and Wales to the ferry at Holyhead. Leaving the rental car there and picking up a rental car in Dublin for a circuit of Ireland and ending up turning in the car at Dublin and flying home. What problems might we encounter?
I'm not sure what you are asking. Problems with timing? With renting? With traveling by car? Please give us a few specifics so we can answer your question. How long is your trip? What time of year are you considering? What are your interests? What is your budget? What is it that you are concerned about?
We are looking at late May early June. I'm concerned about the logistics of renting in London, dropping off at Holyhead, renting agian in Dublin. We did this kind of thing in New Zealand with great results.
We did a similar trip ten years ago. Drove to Holyhead from Stoke-on-Trent area. At that time there was some road construction and lots of truck traffic along the way. We had arranged for an early am crossing on the ferry and had to spend a night in HH. Had no room reservation and had to stay at a really awful place. It is not an attractive town. We turned in our car at Hertz right there near the ferries (very easy & quick) and our ferry crossing was very pleasant. Driving in Dublin is not easy.
Don't drive in Dublin, use public transport which is great and use car for the rest of Ireland.