Brussels - Britain and the EU kick off a third round of Brexit talks on Monday, with London impatient to agree its future relationship with the bloc while Brussels insists the divorce settlement comes first.The European Union's chief negotiator Michel Barnier will meet his British counterpart David Davis late afternoon in Brussels for a first exchange, followed by three days of discussions and a joint press conference.The EU says there has to be "sufficient progress" in three key areas - EU citizen rights, Northern Ireland's border and the exit bill - before it can consider London's demand for talks on future ties in October.Britain says it would be best to negotiate the two in parallel and that settling trade issues may even help with other problems such as the future EU-UK border between Northern Ireland and the Republic.That is a complete no-go for Brussels which made no secret of the fact that it expects little progress in bridging what officials last week called a "very big gap".'Lack of substance'They also blamed Britain for a "lack of substance" despite a flurry of position papers they said were strong on aspiration but short on detail.Barnier last week listed on Twitter the EU's own negotiating documents, noting: "EU positions clear and transparent since day one."Davis said on Monday the British papers were "products of the hard work and detailed thinking that has been going on behind the scenes and should form the basis of what I hope will be a constructive week of talks"."We're ready to roll up our sleeves and get down to work once more," he added.Both sides have repeatedly warned that the clock is ticking down to the March 2019 Brexit deadline and that they are the ones doing their best to make progress.The situation is complicated by sharp divisions within Prime Minister Theresa May's Conservative government after a June election gamble backfired and she lost her parliamentary majority.May remains in office thanks to a deal with Northern Ireland's ultra-conservative Democratic Unionist Party which views the Republic with deep suspicion.EU officials warned last week that the hard-won Northern Ireland peace process could not be used as a bargaining chip.RightsAs for London's suggestion that technology could help prevent the border becoming a barrier to trade and the peace process, that was just "a lot of magical thinking", one EU official said.In another position paper, Britain said the European Court of Justice might continue to have an indirect influence, softening its position that the EU's top court would not have any say in the country at all.But again this was not enough, EU officials said.The rights of more than three million EU citizens in Britain and one million Britons in Europe arose from EU law which is the remit of the ECJ, they added."There is no other possibility," one official said.As for Britain's divorce settlement - estimated at up to €100bn ($119bn) in Brussels but much less at €40bn ($47bn) according to reports in London - the EU officials said the talks were not about fixing a number but about agreeing how to work out the bill."We have to have a methodology sufficiently detailed so that commitments made to various beneficiaries of the EU budget will be honoured," one of the EU officials said.In what the European Commission insisted was "absolutely nothing extraordinary", former British premier Tony Blair is due to meet Commission head Jean-Claude Juncker on Thursday as the Brexit talks wind up.The British press made much of the visit as Blair is staunchly pro-EU and anti-Brexit, and has campaigned for a second referendum in the hope of reversing the June 2016 outcome.