In her Mansion House speech on 2 March 2018, May performed a balancing act between hailing national sovereignty and shielding British jobs and manufacturing from using that sovereignty to diverge. Avoiding a negative economic impact by preserving supply chains, which was one of her tests for a good deal, required UK alignment to EU rules on goods, she thought, but as a compromise to avoid ruffling feathers with pro-Brexit members of her cabinet, the prime minister proposed “managed divergence” from EU rules. Civil servants in Whitehall dubbed it a “reverse Ukraine” agreement. Whereas Ukraine had committed to converge with the EU to gain correspondingly more market access over time, the UK wanted to diverge and accepted a gradual loss in ease of access to the EU market. There were three avenues for gradual divergence, May put forward. Sometimes the UK Parliament would adopt identical laws as the EU and UK courts would ensure consistency with the jurisprudence of the EU Court of Justice in such cases. Sometimes UK laws would achieve equivalent outcomes via different means and sometimes the UK would do its own thing. May gave the digital industry as an example of the latter. The outcome would be frictionless trade on goods with the EU, despite the UK's departure from the single market and customs union. Her Lancaster House speech a year earlier made that pledge of frictionless trade already. Now she proposed a method to get there, nicknamed “the three baskets” by commentators.

Apart from objecting on principle to giving the UK free movement of goods without free movement of people, which contradicted the Barnier staircase, the EU perceived a bureaucratic monster for the sole benefit of the UK. EU–UK committees would have to meet constantly to assess whether unilaterally decided UK rules diverged, with a potential for endless controversies and formal disputes on which rules were equivalent and which ones were not. Trade and businesses would face constant uncertainty. A bespoke deal was “administratively crazy”, the late Henrik Enderlein, a Berlin-based professor of political economy and director of the pro-EU Jacques Delors Centre, tweeted, whereas the Norway model was “politically crazy” for a large economy like the UK, which could hardly become a rule-taker.