Thanks for all the advice (its much appreciated) and sorry if I caused any offence. Fwiw I agree about taking the structure back to the ground entirely. The cost of this would run well up to £10k. Perhaps more. Perhaps the SE will lend a hand on the concrete breakers??? Does their insurance cover for mistakes like this? Before the threaded bar was used quite a number of phone calls were made by the prinicipal contractor to the SE and roofing engineer who both gave the go ahead for these undersized anchors to be used. God knows why. The ones we have now are 30mm grade 8.8. Which I believe has a tensile strength of around 150,000 pounds per square inch.