National Australia Bank said yesterday that it will offer to buy back its March 2012 government guaranteed bond line. The bank has A$3 billion on issue in this line, in floating rate and fixed rate notes.The bank paid a margin of around 130 basis points over swap for the funds when they were sold, in several instalments, in early 2009.The debt must rank as expensive for the bank, taking into account the fee of 70 basis points for the government guarantee.This may be the first buy-back of government guaranteed debt by a bank since the scheme was introduced in late 2008.