As Sir Mervyn was at pains to emphasise, this is not a simple matter of "in or out" - or even, in David Cameron's rather undiplomatic phrase, "make-up or break-up".
It is remembered for what is defined as an undiplomatic mis-step rather than the pictures of moist and over-lengthy handshakes that they are convinced will be so appealing to viewers back home.
To spring a prohibition on foreign financial institutions offering forex trading to U.S. customers as of Oct. 18, 2010 (the effective date of the new CFTC rules) would be extremely undiplomatic on a global country-by-country dealing basis.