Google doesn't know how narrow the roads are, how much traffic you could encounter, where the roadworks are, and where you could get a little lost.
I agree that England, Ireland,and Scotland are too much for 2 weeks. How about just England and Scotland, leave Ireland for later? Glasgow and Edinburgh are less than an hour apart on the train, so that would be easy. On the bus you could also go to Stirling to see the castle (more interesting than Edinburgh Castle, in my view). On the bus from Glasgow (or by car) you could get to Fort William in the highlands. We did a day trip to St. Andrews from Edinburgh on the bus--very interesting but no need to stay overnight. London to Scotland you could fly cheaply on easyjet or else take the train.
