Riskier Mortgage Bonds Thrive Off U.K. Pandemic Property Boom

The business of mortgage securitization is getting a jolt from U.K. pandemic aid and a housing boom that’s favoring lower-end borrowers.

Non-bank lenders have sold more than 17 billion pounds ($24.2 billion) of debt pooling non-conforming and buy-to-let loans, the most in at least four years, according to data compiled by Bloomberg. That’s more than double the amount sold during the whole of 2020.

The spike in mortgage securitization in part stems from the Treasury’s tax holiday on property purchases, which is spurring an unexpected homebuying spree in the throes of the pandemic. With more mortgages to fund, lenders ...