Prime Minister Theresa May says she intends to return to Brussels with new ideas on the Irish backstop.   The EU has already dismissed the idea of putting a time limit on the backstop, so what other ideas have been suggested? The backstop: a reminderThe backstop is an insurance policy - designed to avoid a hard border "under all circumstances" between Northern Ireland and the Irish Republic. If the UK leaves the customs union and the single market that could mean goods would have to be checked as they crossed the frontier. The UK and EU would instead like to keep the border frictionless through a comprehensive trade deal. If such an agreement could not be reached, then to avoid those checks with customs posts or other infrastructure, the backstop would come into force. It would keep the UK in a "single customs territory" with the EU, and leave Northern Ireland in the EU's single market for goods. Many MPs fear the UK could be "trapped" in that arrangement for years, leaving it unable to strike its own trade deals on goods with the rest of the world. The prime minister's Democratic Unionist Party (DUP) allies also do not want to see Northern Ireland treated differently from the rest of the UK. So what could be done? Clarification - and another referendum The Irish economist Karl Whelan has suggested that the EU should clarify that it has no objections to Great Britain leaving the customs union backstop while Northern Ireland stays in it. "This is the original version of the backstop that the EU offered, so it should be clear they are willing to still offer this," says Prof Whelan. That would leave Great Britain free to strike trade deals but Northern Ireland would not be part of them. That would be anathema to the DUP and other MPs. he second part of Prof Whelan's plan is to use the Brexit political declaration to promise the citizens of Northern Ireland a referendum on the backstop, should it ever come into effect. He suggests that five years after the beginning of the operation of a Northern Ireland-only backstop there would be a vote on whether to remain within the EU's customs union and single market. He says: "A promise to hold a referendum five years after the end of the transition period would provide a clear concession to those who believe the backstop arrangements would be harmful to Northern Ireland by offering them a chance to convince their fellow citizens to end the arrangements after a period."   AFP.