Recent high-profile collapses of high street names such as Comet, Phones4U and other companies have left thousands of people out of work and have cost the taxpayer millions in statutory redundancy payments and unpaid taxes. This week File on 4 goes behind the headlines to examine the role of the companies' private equity backers. Were these failed businesses which were bound to have to close? Or might they have survived for longer under different ownership? Fran Abrams investigates.