You are correct in looking at clause 80.1, however it is the first main bullet that you should be looking it as this concerns ‘claimed, proceedings, compensation and costs payable’. And the reason would depend on why the accident happened - if it was a fault of the Employer’s design whatever Contractor had built it, it would be the Employer’s risk.
However, if it was because of something which could be linked back to the Contractor, then it might well be the Contractor’s liability. If it was a mixture, then the indemnity clauses of 83 would come into play (or if it was the fault of the Contractor, but they sued the Employer and vice versa).
Do note that the PM could have (past tense) changed the Works Information to avoid takeover under clause 35.2.