Be careful, the UK's total external debt has exceeded 10 trillion[0]. We have huge financial sector debt here and are worse exposed to financial shock from the banking system than almost all countries globally.
Agreed that getting out of the USD hegemony is inevitable. As to whether it will be an orderly transition, I'd say that is far from assured, especially in the UK.
[0] http://en.wikipedia.org/wiki/List_of_countries_by_external_d...