Warren Buffett’s Berkshire Hathaway went ahead with plans to set up a new bond insurance company last month, just weeks after receiving an unusual call from New York state’s insurance regulator urging it to enter the multi-billion dollar market.

The move by Eric Dinallo, New York state’s superintendent of insurance, was made amid concerns that losses by Ambac, MBIA and other bond insurers, related to their exposure to risky subprime mortgage bonds, could damage their top, triple-A credit ratings.