Pension funds in the UK are nearly three times as likely to go bust if their parent company is less creditworthy, according to new research, illustrating why pensions trustees make punitive payment demands of heavily-indebted buyers - such as private equity groups - which acquire their companies.

Trustees at the pharmacy Alliance Boots last June forced private equity firm KKR to stump up a £1bn (€1.5bn) package for their pension scheme, adding about 9% to the £11.1bn price tag for the deal.