A promiment British newspaper today revealed an article about the problems encountered by tourists flying into the Southern Ireland and travelling in Northern Ireland.
Personally I never considered this matter as I figured that most tourists were educated and intelligent enough to realise that Northern Ireland is in fact the United Kingdom and only by the fact it is attached to Ireland is why its called Northern Ireland.
They said that shopkeepers have been going blue in the face with tourists paying for items in Euro and not understanding that Euro is not accepted in the north. The tourists actually thought that Northern Ireland was in fact just a province of Ireland even though we all know its Ulster.
Police at the same time are being shocked at the speed of people on motorways and regional roads. They cannot understand why the tourists are driving so slow until they pull them over. This is as most of the signs in the North do not display that the speed is MPH. They simply just state the speed.
This is the TA opinion on the cross border:
There is no discernible border between the Republic of Ireland and Northern Ireland so no passport is needed when driving from one country into the other. Be aware, however, that once you cross the "border" into Northern Ireland speed limits and distances will be shown in miles (kilometres in the Republic). Northern Ireland uses pounds sterling, the currency in the Republic is Euro.
You must also check that you car rental Insurance covers you to leave the country. Irish rental Insurance has no jurisdiction in the UK so you may not be covered unless otherwise stated.
Your phone card will not work in the north.
Your money will most of the time not be accepted unless on border counties and towns.