The transfer of Northern Rock to public ownership has been completed after Chancellor Alistair Darling signed off its nationalisation.
He was able to make the order shortly after Parliament approved emergency legislation to allow such ailing financial institutions to be taken over by the state.
Downing Street confirmed that Ron Sandler, the City troubleshooter chosen by the Government to head the new operation was now in place.
Prime Minister Gordon Brown's spokesman said: "Ron Sandler has formally taken up his position. He will appoint his board and conduct his strategic review."
The Treasury confirmed it had acquired all of the shares in Northern Rock. MPs have 40 sitting days to lodge an objection to the nationalisation order.
The emergency legislation will now pave the way for a compensation scheme to be set up for shareholders, under which an independent valuer will be appointed to decide on the level of payout.
An order for the scheme will be laid before Parliament shortly, added the Treasury.
The formal transfer of the bank's shares comes at the end of a whirlwind three-day rush to push the legislation through Parliament.
It was finally approved late on Thursday night when opposition parties abandoned an attempt to make the troubled bank subject to freedom of information (FOI) laws.
Ministers insisted such a move could damage the bank's commercial interests and pointed out that the nationalisation was intended to be a temporary measure.
