Clearly, the scale of payments will increase as more projects are signed. However, it is impossible to estimate with any certainty what the public sector costs will be when the schemes currently in procurement are completed. One crude method is to examine the ratio of capital values to long-term unitary charges on schemes that are signed. As noted, the value of schemes signed as of March 2008 is £1.29 billion, and public sector liabilities on these schemes are £4.69 billion in nominal terms, giving a ratio of 3.64. Adding the projected value of schemes currently in procurement produces a total capital value of £3.22 billion - and multiplying this by 3.64 yields the figure £11.73bn.
Given the numerous sources of measurement bias2, this figure is not very meaningful. Perhaps all we can currently say is that, by 2012, the total cost of PPPs in NI will be in the range of £10-15 billion.
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2 For example, past experience shows that both capital and contract costs on PPPs increase during the procurement process, so it cannot be assumed that the currency quoted costs are accurate.