Factbox - How can Britain avoid a post-Brexit border for Northern Ireland?

LONDON/DUBLIN (Reuters) - Britain said on Wednesday there should be no border posts or immigration checks between Ireland and the British province of Northern Ireland after Brexit, in a paper that attempts to resolve one of the most complex aspects of its departure from the European Union. Here are some of the main details of the British proposals: BORDER INFRASTRUCTURE Britain reaffirmed its opposition to a "hard border" with passport and customs checks and said there should be no physical border infrastructure of any kind across the 500-km (300-mile) border. It acknowledged that modern technology alone could not replace the traditional checks and that instead a deal would require "a political and not just a technical solution". While there won't be surveillance infrastructure at the border, electronic tagging of cargoes is a possibility. It also rejected the idea of an effective customs border in the Irish Sea that separates England, Wales and Scotland from Ireland and Northern Ireland - something advocated by Ireland - as "not constitutionally or economically viable". The proposed "frictionless and seamless" frontier is, however, heavily dependent on Britain convincing the EU that an open border with EU member state Ireland will not compromise the single market. The paper appeared to hint at a compromise in which the EU would offer a waiver on certain goods entering the EU single market from Northern Ireland, for Britain to enforce EU standards on some goods and for Ireland and Northern Ireland to synchronise regulatory standards in some areas. IMMIGRATION The planned continuation of the Common Travel Area between Britain and the Republic of Ireland, which has been in place for most of the period since Irish independence in 1922, means that checks will not be required for Irish or British citizens. The paper said there are just a handful of countries that require visas to either the United Kingdom or Ireland and not the other. However, Ireland is obliged under the EU single market to allow free movement of EU citizens to Ireland, creating an effective back door for EU nationals into the United Kingdom. The paper said that Britain was confident that, in lieu of border posts, migration of EU nationals via Ireland could instead by controlled by restricting their right to work legally and access the social security system in Britain. The proposals could annoy some British voters who said controlling immigration from the EU was a key reason for backing Brexit. TRADE Britain suggested a waiver for smaller traders who "cannot be properly categorised and treated as economically significant international trade", noting that in 2015 more than 80 per cent of North to South trade was conducted by small and medium-sized businesses. Larger businesses could apply for "trusted trader" status, which could allow for simplified customs procedures, such as reduced declaration requirements and periodic duty payments. It called for a robust enforcement mechanism to ensure that goods which did not comply with the EU’s trade policy stayed in the UK, possibly including a tracking mechanism and a system whereby tariffs would be paid later depending on the final destination of the goods. It also called for waivers from security and safety declarations, and ensuring there is no requirement for product standards checks or intellectual property rights checks at the border. The document also called for an exemption to allow the free flow of agriculture and food products across the border, noting that the island of Ireland was already acting as a "single epidemiological unit" with regards to animal infections such as foot and mouth disease. The proposals would require significant concessions from the European Union and any enforcement of EU standards is likely to face opposition from Brexit supporters opposed to regulation from Brussels. [The full document is available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/638135/6.3703_DEXEU_Northern_Ireland_and_Ireland_INTERACTIVE.pdf] (Reporting by Conor Humphries; Editing by Guy Faulconbridge and Gareth Jones)