Ministers have set a target of 170,000 new affordable homes in the next two years. But the Housing Associations which must take a major part in delivering them are under increasing financial strain.With their incomes squeezed by benefit reform and grant cuts, many are taking a more commercial approach. But there's concern some are taking too many financial risks.And MPs have voiced fears that the regulator charged with monitoring the associations' viability is not up to the job.Fran Abrams investigates.Reporter: Fran AbramsProducer: Nicola Dowling.