What is the consequence of accepting the Contractors Design? Should the WI be amended if for example an alternative specification has been proposed and approved by the PM?
It needs to be made clear that the Project Manager is clearly accepting that the proposed design is an alternative to that proposed in the original Works Information. If not, there will remain an ambiguity/inconsistency within the documents which could be picked up on at a later stage. Clause 14.1 makes it clear what liability the Project Manager is taking on when they accept a design, and that is not errors/mistakes that they have not spotted that do not comply with the Employers original works information.
In your example the best way to deal with this would be to accept the design, and also issue an instruction changing the original Works Information so that there is no ambiguity/inconsistency between the documents. Any such instruction is normally a compensation event, but this would be an exception to that rule (identified in 60.1(1)) as this instruction would be to make a change at the request of the Contractor to comply with their proposed design.
The main point to address is that you should not “assume” that however clear you think you have made your submission to change the original Works Information that when he accepts the design by default he is agreeing to your proposed changes. You do not want an ambiguity.inconsistency to remain or potentially be abused at a later stage of the project.
I would like to add or perhaps emphasise that the Works Inforamtion (very much like the Programme) is both a tool for looking forward to what will be done AND a record of what has been done, the later being very important when you look at the definition of a defect for example. The Works Inforamtion MUST therefore be clear as Glenn says but MUST also be an accurate relfection of what is to be done and has been done so far.
As Glenn says, the cost and time conseqeucnes will be deterimed by whether the facts fall withinnteh scope of 601.(1) (I think your question is ambiguous as to whether this is design and build or traditional, I think Glenn has assumed D&B) but that should have nothing to do with whether the Works Information should be updated.