This is not a worked through set of ideas and is merely intended to provide some food for thought as David Davis has called for blue sky thinking.
Agree as an interim package that:
1. Britain will remain in the single market and customs union – which would also solve the problem of maintaining an open border with the Republic of Ireland and take any remaining wind out of the sails of Scottish nationalism, thereby preserving the relative market size of the UK in any future trade negotiations as part of the EU or outside it. For a brief explanation of the existential significance of the relationship between ‘relative market size’ and ‘integration’ please see my recent post, ‘What is the Single European Market?’: https://www.linkedin.com/pulse/what-european-single-market-carl-islam;
2. instead of payment of a divorce bill, Britain continues to pay its full annual contribution to the EU budget throughout the duration of the interim period;
3. all EU nationals currently resident in the UK can remain (including their families);
4. all EU nationals who are deemed to meet qualifying criteria, are free to move to the UK and remain here at the end of the interim period, e.g. those working for a recognised employer e.g. the NHS, a University, or company (including the financial services industry);
5. all other EU nationals seeking to move to the UK may do so if they meet certain criteria e.g. income, savings and health insurance for an initial period of two years before they can claim health and welfare benefits;
6. there are specific carve-out rules e.g. for students paying for education in the UK;
7. during the interim period the EU examines its freedom of movement policies and rules with the aim of reforming them to enable greater control by each sovereign member state in accordance with uniform criteria (i.e. to restore border control);
8. the interim period end after policy reform has been voted on by each member state, subject to a specified long-stop end-date;
9. following publication of the decision reached by the EU about reform of freedom of movement, a referendum be held about whether Britain should remain a full member of the EU or negotiate an orderly exit within a period that is sufficient for the civil service to put in place practical implementation plans e.g. about customs, ports, and air safety, and for businesses to adjust.
Would this provide business with the certainty is needs in order to undertake long-term planning? If not, and businesses decide that it is better to go now rather than in e.g. 4-6 years time, the package will not avoid the adverse economic consequences of a hard Brexit.