But Conservative Brexit spokesman David Davis has said that should the people of Northern Ireland ever vote to leave the UK , they would "be in a position of becoming part of an existing EU member state, rather than seeking to join the EU as a new independent state". It would then be up to the EU Commission "to respond to any specific questions about the procedural requirements for that to happen," he added. But Mr Davis said the UK government's "clear position is to support Northern Ireland's current constitutional status: as part of the UK, but with strong links to Ireland". Labour leader Jeremy Corbyn says there should be a referendum on Irish unity if the Northern Ireland Assembly wants one. The issue has been further complicated by Theresa May's deal with the Democratic Unionist Party, enabling her to form a minority government, which some critics, including former Tory Prime Minister Sir John Major, have warned could adversely effect the peace process and mean the UK government would no longer be seen as an "impartial honest broker" in restoring the power-sharing arrangements and upholding Northern Irish institutions. How much has Brexit cost so far and how much will it cost by the end? There is much debate about the long-term costs and benefits to the UK economy of Brexit - but what we do know for certain is that the EU wants the UK to settle any outstanding bills before it leaves. There have been no official estimates published of the size of the bill, which covers things like pension payments to EU officials, the cost of relocating London-based EU agencies and outstanding EU budget commitments. Various figures ranging from 50bn (£44bn) best online shopping websites to 100bn (£88bn) euros have been bandied about but although the UK has agreed to meet its financial obligations, Brexit secretary David Davis has said: "We will not be paying €100bn." The UK could leave without any Brexit "divorce bill" deal but that would probably mean everyone ending up in court. If compromise can be achieved, and if payment of the bill were to be spread over many years, the amounts involved may not be that significant economically.