A conceptual analytical approach can be used to model the scale of the affordability problem. The dynamics of cost and time within the EPP can be simulated using simple mathematical modelling. As described in the cost of delay analysis in Chapter 7, delays to projects (whether driven by budgetary constraints, technical difficulties, time mis-estimation or some other factor) will give rise to additional costs, demanding 'inefficient' spend that does not directly contribute to delivering the required capability. For instance, delaying a project means that the IPT will be running for longer than originally anticipated and industrial capacity previously earmarked for the project may lie idle (or be used in less efficient ways). Money spent meeting the associated costs will necessarily be unproductive.
Depending on the drivers of 'inefficient' expenditure, in one extreme it is possible that this spend will have to be consumed immediately. Alternatively, in the other extreme, this additional expenditure will be deferred across the lifetime of the project. For example, spend on additional net support costs will not be incurred until after the original ISD. A significant proportion of these costs will find their way into the EPP over time, in the form of modest, but relatively continuous increases in the cost to completion.