James Lockhart’s successor as director of the agency that regulates Fannie Mae and Freddie Mac will hold much of the US mortgage market in his hands when he takes the helm.

Government-backed mortgage financiers Fannie and Freddie own or guarantee 73 per cent of new mortgages in the country and 56 per cent of all existing single-family mortgages. The companies were taken into their regulator’s “conservatorship” last autumn, after mounting mortgage losses eroded their capital cushions and raised fears of collapse.