On the French interconnector and on the Dutch interconnector (and probably on the Irish ones too) it is *impossible* to trade export to the point where it affects system margin in the UK.
If you mean all of it then that is not classed as a credible fault.
64GW is also around 10GW *above* the currently predicted max demand this winter (1 November 2012 to 28 February 2013) although we peaked at around 55GW levels yesterday and the predicted peak tomorrow is nearly 58GWAs I've said previously this winter isn't going to be a problem and given a triple dip recession we are possibly secure for a few more winters to come...