LONDON, United Kingdom — The UK's Pensions Regulator has stepped up efforts to require retail magnate Philip Green to plug gaps in the pension plan of department-store chain BHS, which failed a year after he sold it.

The agency has “formally begun enforcement action to seek redress,” it said in a statement Wednesday. It sent notices to Green and his investment vehicles, as well as to Dominic Chappell, a former race-car driver with no previous retail industry experience who bought the chain from Green for 1 pound in 2015.

“Our decision to launch enforcement action is an important milestone in our work to attain redress for the thousands of members of BHS schemes who have been placed in this position through no fault of their own,” the regulator’s chief executive officer, Lesley Titcomb, said in the statement.

BHS, formerly known as British Home Stores, collapsed in April with a pension deficit of at least £571 million. The failure cost 11,000 jobs and threatened the pensions of more than 20,000 former employees.

Green, a billionaire who also controls Top Shop and other retail chains, said he had already made a “credible and substantial proposal” to support BHS pensions, aiming to keep them from falling under the UK’s Pension Protection Fund, an insurance system.

“This is in order to achieve a better outcome for the BHS pensioners,” he said in a statement.

The House of Commons last month supported a measure calling for Green to be stripped of his knighthood. A committee overseeing such honours has yet to act on the recommendation.

By Eric Pfanner; editors: Benedikt Kammel and Matthew Boyle.

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