[QUOTE=KenJohn;8323129]There are not passports checks between the UK and Ireland. While a UK visa is no strictly valid in Ireland, no one checks when you travel between the UK and Ireland. You do not need both an Irish and a UK visa for vacationing.[QUOTE]
The one exception to this of course is when passing through Heathrow from one terminal into Terminal 1 en route to Ireland, in which case you must pass British immigration in the FCC, and you will be treated just as if you are entering the UK and must fill out a UK landing card.