This treaty is now in legal limbo and cannot come into force without American ratification.
The No 10 spokesman admitted this means that no royal charter could come into force without the agreement of Clegg.
Regulations become law in all member states the moment they come into force, without the requirement for any implementing measures, and automatically override conflicting domestic provisions.
The UN Convention on the Law of the Sea, for example, came into force without US ratification.
FATCA, which is due to come into force in July after several delays, has supercharged the expansion of a network of bilateral tax-information accords, leaving the tax-shy with far fewer places to hide.
Normally they come into force in January, but this year they were delayed until 1 July - apparently so as not to influence the outcome of the presidential election.
The plan was meant to come into force in January 2014, but will likely be delayed by a few months at least.
If Britain votes to remain in the EU, ministers hope the emergency brake could come into force in six to nine months, although the deal's fine print suggested the delay could be closer to a year.
Formal consultation over the plan has been delayed until the spring, so the system might not come into force until October 2013, six months later than planned.
His claims, which have been strongly denied by the LAA, provoked fury among solicitors' groups, who have protested over the delays over awarding the contracts which are due to come into force in January.
The policies come into force from January 1 2019.
