Concern at Rock's off-balance-sheet vehicles

Confusion arose last night over whether the nationalisation of Northern Rock could result in the Government running its own offshore, off-balance-sheet vehicle – an arrangement ministers have lambasted private sector firms for using.

Separately, opposition MPs expressed concern about whether the Government has lost control of the better part of the Northern Rock mortgage book to an offshore trust, being left with the "rubbish", in the words of the former Tory chancellor Kenneth Clarke.

In its latest statement of the treatment of Northern Rock in the national accounts, the Office for National Statistics said "some parts" of Granite, Northern Rock's off-balance-sheet "special investment vehicle" or SIV, will be visible in the public accounts: "ONS judgement was to classify to the public sector the UK-resident special purpose vehicles used in the securitisation programme." But those parts of Granite that are offshore (registered in Jersey) will effectively be off the public sector's balance sheet – even though they are potential liabilities for the taxpayer.

Granite is used by the Rock to securitise its mortgages. It is split into three entities. One company issues bonds, and is registered in the UK; a trust company holds the mortgages and is registered in Jersey; another group of companies move money between the others and are partly registered in Jersey. The trust has £45.7bn of securitised mortgages.

Such arrangements jar with the Chancellor Alistair Darling's recent remark that "there needs to be better regulation to stop banks hiding things off-balance-sheet".

However, Yvette Cooper, the Chief Secretary to the Treasury, said Granite was a "separate legal entity, which will not be covered" by nationalisation. Philip Dunne, a Conservative MP, said: "Northern Rock retains a seller's share in the packages of mortgages provided to Granite to provide security for the debt obligations that Granite issues." Those mortgages, he said, must be "refreshed continually" with a new supply of mortgages from Northern Rock, or "liabilities will crystallize, there will be a default."

The Rock sold half its mortgages to Granite between 1999 and September 2007, but Mr Darling said it still had "high quality" assets.