Arguably, this innovation can also go ahead without treaty change.
But some diplomats are considering improvements that could be made without treaty amendment.
With or without treaty change, the euro zone is being forced to centralise powers.So what of the ten outs?
The third option could be implemented swiftly without treaty change while the first would take years and substantial treaty change, experts said.
But it is hard to see how such ambitious ideas could be implemented without treaty changes unanimously approved by the 27 E.U. states.
However, the fact the changes were agreed without recourse to rewriting EU treaties may also give hope that the British government could achieve EU reforms of a similar scale without treaty change.
Rule change is still possible without treaty change but the French position makes it more difficult for the prime minister to make fundamental and significant reforms of the sort demanded by eurosceptics.
Eurosceptics believe their case has been strengthened after Downing Street accepted at the end of last week that the referendum would take place without treaty change enacting the reforms that Cameron wants to achieve having been ratified across the EU.
Nicolas Véron, an economist at Bruegel, a policy research group, argues that some of this can be done without treaty change — for example, providing supranational guarantees to national deposit insurance programs, to forestall the risk of catastrophic runs on consumer banks in troubled countries.
Cameron was already wise enough to ask for largely cosmetic changes that can be delivered without treaty change, just as the Labour prime minister Harold Wilson did when he pioneered the same "renegotiation" strategy ahead of the 1975 referendum on British membership, and for exactly the same reasons of party management.
