2 week trip to England and Ireland

I can't speak to which will be cheaper- but be aware that some car rental companies in England specifically prohibit you taking them on the ferries.

It seems to me that Rick has always reccommended renting a car in each place. I agree with Toni's point about some companies not allowing you take their cars into Ireland. I don't know if it still holds true, but there was a time when if one had a platinum credit card it covered your car rental insurance in other countries...except Ireland ( and a couple of others). I think it had to do with the Irish rather cavalier attitude toward having auto insurance.

You're probably better off renting in each place. During "the troubles" such an idea would have been completely forbidden but even now it wouldn't be your best option I don't think. Ireland is treated differently than most countries - many credit card special 'car rental insurance' is void in Ireland - and your insurance rates may be different for the entire rental if you do this. I did this recently and from a practical standpoint I actually found being able to shop for different deals in the two countries allowed me more freedom. Also the time without a car in between was a nice break. We started in England and the with several days in Dublin and the is no reason to have a car in Dublin so we did 5 days in England with a car - a few days without and then Dublin without - and then rented a car at Dublin airport for driving around Ireland. From my experience a car in Dublin would be an expensive burden so save those car rental day charges - you'll need them to pay for dinners out in Dublin - and only rent a car when you really need it. The airporter buses in Dublin are fast and efficient and picking up a car at the airport means you're already out of the city and near the freeway.
Have a great time!

Thank you all very much, My husband has listened to the hints and is re-thinking our car rental dilemma.

Do you have your tickets yet? If not, can you fly open jaw, say into London and home from Dublin? Also agree with not having car in Dublin, use public transport, same with London.

" I think it had to do with the Irish rather cavalier attitude toward having auto insurance." I believe it actually had more to do with the ease with which people unaccustomed to driving on narrow, stone-wall-bordered roads, accompanied by farm equipment and animals, could get into accidents. I have never heard anything about the Irish having a "cavalier attitude" about having car insurance.