See here.
http://www.cml.org.uk/cml/policy/issues/107
Some pre-fabricated housing designs were later deemed defective. It is often to do with corrosion of the steel bars in the pre-fabricated slabs. PRC is a subsidiary of the NHBC scheme that warrants the structural integrity of new houses. As far as I know, all pre-fabricated house designs went through a review and some had remedial action to them. You will need to find out what manufacturer your house is, and presumably the council can tell you that.
This is actually an issue for the seller of the house (who I assume is not the council). They need to prove that the house is either not a defective design or that inspection/remedial action was undertaken and a certificate issued. Most of this remedial work was done in the late 1980s. Don't buy the house otherwise (your mortgage lender won't let you anyway).