Theresa May’s letter stated that H.M. Government seeks “a deep and special partnership” with “a bold and ambitious Free Trade Agreement” that covers financial services, where we “have to align with rules agreed by institutions of which we are no longer a part”, and “manage the evolution of our regulatory frameworks to maintain a fair and open trading environment”.
The closest model would seem to be the Deep and Comprehensive Free Trade Agreements (DCFTAs) that the EU has already negotiated with Ukraine, Moldova and Georgia, and has offered to Tunisia, Morocco, Egypt and Jordan. Since all these jurisdictions account for a smaller share of EU exports than the UK, (e.g. Ukraine’s share is 0.8% against the UK’s 8%), it is realistic to expect similar terms to be readily offered to the UK.
A “no deal” scenario on Brexit was never taken seriously by the EU institutions, and is not on the agenda. Exiting with no agreement on terms of departure or successor trade deal at all would harm the UK’s prospects of securing favourable future trading arrangements not only with the EU, but also with other countries. It would probably result in British GDP falling by something like £1,700 per household, thereby risking tainting the Conservative Party with economic mismanagement. Had Mrs May seriously sought or expected a “no deal’ scenario, she would not have wasted political capital and risked her credibility seeking to negotiate a new trade agreement alongside an exit deal; it would rather have been to her advantage to leave more quickly and suffer an economic shock in 2017, in the hope that the economy was reviving by the time of the next election.