It is perhaps an implicit acknowledgement of how little attention the campaigners for Brexit paid to the actual mechanics of leaving the EU, and how disastrous that lack of attention turned out to be, that those same campaigners, now agitating for the UK to leave the ECHR, are at least trying to think through the mechanics of doing so.
The Prosperity Institute's paper that addresses that issue is of the quality one would expect from a paper authored by Suella Braverman, Boris Johnson’s former Attorney General, whose advice on the international law implications of his government’s proposals to legislate to breach the Ireland/Northern Ireland Protocol (now the Windsor Framework) that Johnson had only just signed was almost universally regarded as hopeless. The paper has not been improved by the apparent assistance of Lord Frost, the UK’s former ambassador to Denmark, and the man whose negotiating skills led the UK into two of the three international treaties that the paper now spends much energy trying to wriggle out of.