Shares in Thornburg Mortgage fell more than 5 per cent on Wednesday as the provider of so-called “jumbo” mortgages said it had received subpoenas from US securities regulators and raised doubts about its long-term survival.

Thornburg, which specialises in large mortgages that typically go to buyers of more expensive homes who have good credit histories, nearly went bankrupt in March and last week posted a $3.3bn first-quarter loss as the value of mortgages and other securities it owns plummeted.