UK government looks to sell senior protection

Yesterday the UK Treasury announced that it plans to offer protection against credit losses to banks above a first-loss threashold - in effect, taking the senior tranche of a synthetic CDO - in exchange for a fee.
The announcement says that UK banks (including UK subsidiaries of foreign banks) will be able to buy this protection. The assets must be on the bank's balance sheet and can include residential and commercial property loans, structured credit assets, asset-backed securities, corporate loans and "any closely related hedges" - presumably meaning credit default swaps providing exposure to these assets.
However, the statement does say how the "protection" will be documented - whether though a guaranty, credit default swap or insurance policy. Nor does it say how losses will be defined and what credit events will trigger a protection payment.