If you have followed the debate on the ECB as a lender of last resort you probably came across Article 123 of the Lisbon treaty. Article 123 prohibits the ECB from purchasing bonds directly from public bodies. Paragraph 1 says:
1. Overdraft facilities or any other type of credit facility with the European Central Bank or with the central banks of the Member States (hereinafter referred to as ‘national central banks’) in favour of Union institutions, bodies, offices or agencies, central governments, regional, local or other public authorities, other bodies governed by public law, or public undertakings of Member States shall be prohibited, as shall the purchase directly from them by the European Central Bank or national central banks of debt instruments.
However Paragraph 2 allows the ECB to purchase bonds from a public bank.
2. Paragraph 1 shall not apply to publicly owned credit institutions which, in the context of the supply of reserves by central banks, shall be given the same treatment by national central banks and the European Central Bank as private credit institutions.
(Paragraph 2 was the basis of Soros proposal to transform the ESF into a bank in order to have access to the ECB liquidity. The proposal was rejected.).
Now the key question is who qualifies as a "publicly owned credit institution" described in paragraph 2? At first sight the German Finance Agency (Finanzagentur) qualifies (any one can confirm?). Finanzagentur auctions german debt, through the Buba, using a retention mechanism. The retention mechanism, that came in the highlights with the last November Bund auction, allows Germany to use "the sale of German Government securities in the secondary market that stem from the portions set aside in the auctions" to meet borrowing requirement. According to the Corriere della Sera, the Italian treasury already expressed interest in the retention mechanism as it permits a less risky debt management (if you check the graphs below, you will notice that the last bund auction, where 40% of the bonds have been retained has commanded an average yield of 1.98% when the coupon offered was 2%). Other euro governments might want to follow as well.
(click to enlarge)