LONDON—The business empire of Liberty Steel owner Sanjeev Gupta, including its financing arrangements with bankrupt Greensill Capital UK, is being investigated by Britain’s Serious Fraud Office, the agency said Friday. The SFO said in a statement that it is investigating suspected fraud, fraudulent trading, and money laundering within Gupta Family Group Alliance, including links to Greensill, the supply chain finance firm that went bankrupt earlier this year. Because this is an active investigation, the agency said it won’t be providing any further comment on its probe. Gupta’s companies were among the main clients of Greensill before its collapse in March. Their reliance on Greensill stoked concerns over their financial health when it went under. Liberty Steel, which employs 5,000 people, has sought a government bailout in the wake of Greensill’s collapse. Greensill’s model worked by positioning itself between businesses and their suppliers. It would immediately pay invoices that suppliers gave …