DH and I spent 2 weeks in Ireland in early April 2010, then crossed over to southern Wales, and England. (The Iceland volcano went off shortly after we arrived, but resolved before we went home at the end of the month.)
April, like October, is shoulder season, and there really weren't any tourists. There was some sort of school break, so European families were travelling a bit. We got upgraded everywhere we went, and had great service. Folks were always super friendly and helpful, and we always felt very safe.
One museum in a remote community wasn't open for their season yet, but I still got to explore the ruins on the site.
We have been to the UK twice, and both times had remarkable weather...hot and sunny. The only clothes we never wore was our rain gear. I understand that this is not the norm!
You will have a wonderful trip!
