“Customs and consent” summed up the two sticking points one week before a possibly decisive European Council meeting on 17 October 2019. On consent, the EU agreed that the Northern Ireland Assembly needed to confirm the sustained application of regulatory and customs provisions over time. The UK proposals, however, raised two problems. Frost argued the Assembly should be able to prevent the backstop kicking in, even after the House of Commons ratified it. Such a prior veto right whereby a devolved assembly would overrule a commitment by its sovereign state made no sense for the EU, which wanted certainty that an approved agreement would apply in law and in practice. In addition, in terms of voting procedure, the UK's proposal did not require a majority in the Northern Ireland Assembly. A minority of either unionists or nationalists would be enough to withhold consent. The European Commission refrained from getting too involved in this. Ireland and the UK, as co-guarantors of the Good Friday Agreement, had to clarify the best voting method. UK commentators accused the Commission of misrepresenting the peace accord but this episode at least demonstrates that the EU avoided getting too closely involved in the mechanics of how Stormont would take decisions.

The second sticking point was more of direct concern for the EU. The UK's convoluted system of customs checks – at source as goods left warehouses and companies, and dispersed in various destination points on the island – was unworkable and did not protect the all-island economy. The proposal to exempt small traders opened the door widely to fraud and its heavy emphasis on enforcement underscored for the EU the porous nature of its proposed design. EU practice and law furthermore integrate checks on regulatory standards in customs procedures. The UK could not explain how these checks would work. In debriefing member states, EU experts said the UK ideas did not allow for a proper risk analysis of incoming goods and added that the UK wanted to use customs facilitations for companies that did not qualify under EU rules. Small companies would become automatically “trusted traders”, which meant a better treatment compared to bigger companies that had to qualify for the audited scheme of “authorised economic operators”. This made no sense.