Fears among credit investors have risen that threatened ratings downgrades of commercial property debt might thwart US government efforts to revive the markets that help fund office blocks, shopping centres and other commercial real estate.

Standard & Poor’s warned this week that it was likely to downgrade tens of billions of dollars in triple A securities backed by recent real estate loans – with 90 per cent of the securities backed by 2007 mortgages likely to face rating cuts.

Investors now fear that triple A rated securities backed by commercial mortgages could end up seeing a cascade of rating downgrades, in an echo of the experience of securities backed by subprime residential mortgages.