This is going to have wide-reaching consequences no matter what way it goes. Off the top of my head, potential issues include:
* Combined with the sovereign debt crisis and the migrant crisis, this could be the end of the EU (perhaps unlikely, but)
* The UK leaving the EU with the Republic of Ireland staying in (there's little support for RoI leaving) could create problems in Northern Ireland
* The UK voting to leave the EU, with Scotland having voted to stay, could lead to another Scottish independence referendum
* The UK voting to stay in the EU, with England having voted to leave, might (though I don't know how likely it is) upset people in England
* Whatever way the result goes, it might bring down the current UK Government and force elections
* If the UK leaves, other countries might consider it as well
* If the UK stays, other countries might want to renegotiate their terms as well
* This will bring up the European Convention on/Court of Human Rights, and Human Rights Act, issue again - what happens if the UK actually does leave the ECHR or repeal the HRA? Especially in Northern Ireland, where the HRA is part of the Good Friday Agreement, and in Scotland, where laws must comply with the ECHR
I'm not an expert on any of this. It'll be interesting to see what happens, certainly.
* Combined with the sovereign debt crisis and the migrant crisis, this could be the end of the EU (perhaps unlikely, but)
* The UK leaving the EU with the Republic of Ireland staying in (there's little support for RoI leaving) could create problems in Northern Ireland
* The UK voting to leave the EU, with Scotland having voted to stay, could lead to another Scottish independence referendum
* The UK voting to stay in the EU, with England having voted to leave, might (though I don't know how likely it is) upset people in England
* Whatever way the result goes, it might bring down the current UK Government and force elections
* If the UK leaves, other countries might consider it as well
* If the UK stays, other countries might want to renegotiate their terms as well
* This will bring up the European Convention on/Court of Human Rights, and Human Rights Act, issue again - what happens if the UK actually does leave the ECHR or repeal the HRA? Especially in Northern Ireland, where the HRA is part of the Good Friday Agreement, and in Scotland, where laws must comply with the ECHR
I'm not an expert on any of this. It'll be interesting to see what happens, certainly.