Main Options C and D often lead to disputes regarding the inclusion of staff costs in CE quotations. The basic principle is; the total Defined Cost with the CE less the total Defined Cost without the CE. Although these resources (QS and Design Manager) may be allocated full time, the issue of preliminaries thickening often arises. This is where the effect of numerous CE's, due to additional scope and disruption, requires supplementary resources to be brought in. On it's own this is not a CE, although as Jon Broome has previously suggested, the PM may instruct this as a change to the Works Information, where acting sensibly.
Consider a 'project wide' view of such matters rather than a CE by CE basis and agree a sensible way forward. Many projects now tender a percentage in the contract data to price for this very issue, especially as the nature of Main Option C anticipates change throughout the project life.