DUBLIN (Reuters) - Northern Ireland business groups welcomed agreement on Tuesday between Britain and the European Union on managing the Irish border post-Brexit, but said they urgently need details of how the new trading arrangements will work. The Northern Ireland Protocol - agreed as part of last year’s divorce accord to prevent a hard border between Northern Ireland and EU member Ireland - keeps the British-run region, in effect, in the EU’s customs union and single market for goods after Dec. 31, when the rest of the United Kingdom leaves fully. Exactly how checks, regulations and paperwork will apply is being worked out in talks running parallel to the wider post-Brexit trade negotiations at a joint committee that announced agreement in principle “on all the issues” on Tuesday. In a joint statement, the co-chairs of the committee said agreement had been reached regarding border control posts and entry points, export declarations, the supply of chilled meats and other food products to supermarkets, and on the application of state aid under the terms of the protocol. A meeting of the committee would be convened to formally adopt the draft texts in the coming days and before the end of the year, they said, giving no further specifics on the texts. “Now we need the detail ASAP,” Seamus Leheny, policy manager for the Northern Ireland arm of the Logistics UK trade body, said on Twitter. British-based suppliers and Northern Irish retailers still do not know how the currently frictionless trade between Britain and Northern Ireland will change in 23 days time. Britain’s National Audit Office has said the systems needed to keep trade moving will not be ready in time. British supermarket giant Sainsbury’s, Northern Ireland’s second largest chain, has also warned it will ship across a reduced product range without clarity on the region’s trading status. Northern Ireland businesses have consistently asked for a grace period from Jan. 1 to put in place the new arrangements, fearing they could face more disruption than any other region impacted by Brexit. The head of the Northern Ireland Retail Consortium said that, while Tuesday’s announcement was “hugely positive”, there was still much to do in little time. “Business will need the technical detail of these solutions as soon as possible. Even more than the detail, we will need to see that they work,” Aodhán Connolly said in a statement. “We still need the conclusion of a free trade agreement to remove customs frictions and with three weeks left to go we still will need an implementation period to allow us to comply with the new requirements.”