Alex Dakers, in commenting on this Blog, makes an interesting point that is worth direct posting (so are many other points, incidentally, but I only just thought of doing it this way). He writes:
"There is not an equivalent doctrine of rebus sic stantibus in common law. However, the court-constructed doctrines of "frustration, impossibility and impracticability" other common law countries have achieved the same result.
The modern formulation of the doctrine of frustration can be found in the decision of the House of Lords in Davis Contractors Ltd. v. Fareham U.D.C, since 1956. Lord Radcliffe stated that:
…frustration occurs whenever the law recognises that without default of either party, a contractual obligation has become incapable of being performed because the circumstances in which performance is called for would render it a thing radically different from that which was undertaken by the contract. Non haec in foedera veni. It was not this that I promised to do."We, the people, did not promise to undertake a process that would lead to full political integration. I think Alex has a point.