A regulatory probe into the ownership of UK infrastructure assets threatens to deal a fresh blow to private equity firms, which have ready been finding it difficult to raise money for investment in the sector.

The Office of Fair Trading, the UK's antitrust regulator, plans to review ownership of infrastructure assets, according to a statement. The OFT said it would investigate how the changes and assets' high debt to equity ratios might have affected competition and consumers. Private equity firms traditionally fund deals with two-thirds of debt and the remainder equity.