This is another golden oldie, from the beginning of 2017, before Article 50 notification. It recommended a three-track approach to the Brexit process (a) not getting entangled in discussions of longer term trade arrangements in the Article 50 process itself, (b) sticking with the EEA throughout, and (c) making an immediate start on the reform of immigration/residency policy.
No formalised transition period was proposed in relation to EEA matters, since Art 127 allows for a simple, unilateral withdrawal with 12 months notice. Withdrawal might be triggered in the event that some better, longer-term arrangement could be negotiated or if no accommodation could be found on free movement of workers issues. These were matters that would be determined post-Brexit.
Less sensitive issues — customs arrangements, agricultural and fisheries policies, VAT — would, on the other hand, have required transitional arrangements. Contrary to conventional assertions, an EEA Brexit alone would have been too hard for practical purposes.
In the event, (a) the government sought to make long-term arrangements a priority in the Art 50 negotiations, (b) closed off the EEA track from the outset, and (c) has not made any significant steps forward on immigration/residency policy. That was pretty much the opposite of what was proposed.
GY's political economy blog 