I've done exactly the same thing as Mikeus Ceaser - I wanted to know what would happen if Briton started out as 'civilised' as the Hellenics, but after a few questions on the modding board, decided to just get on a ship and sail the Seleucid royal family over to Ireland.

Playing on VH campaign it's difficult trying to juggle the finances while you make the long voyage. The keys were: Don't take any military units, just family members and peasants. Keep hold of your original territories as long as possible - but don't build anything, and make sure you demolish all the buildings before you do eventually lose them. And most importantly - drop diplomats off on the way and sell those maps! When you get to Ireland, you can take Tara pretty easily with maybe a couple of mercs, then head over to Britain and sack their cities one by one, killing everyone and destroying all the buildings. Once you've done that, take London and all they'll have to take it back is a peasant army. Finally you should be making money, but it's touch and go for a while...

Now, to wait until the Romans are nice and powerful...