The Department may be over-optimistic in its assessment of project costs. The Department’s Cost Assurance and Analysis Service estimates that project costs could be between £5.2 billion and £14 billion higher than those in the Plan. The Department told us that the latter figure was a worst-case scenario and that the different cost calculations are a matter of professional judgement.42 The National Audit Office report highlighted the need for the Department to consider project risks more fully...

The Department may be over-optimistic in its assessment of project costs. The Department’s Cost Assurance and Analysis Service estimates that project costs could be between £5.2 billion and £14 billion higher than those in the Plan. The Department told us that the latter figure was a worst-case scenario and that the different cost calculations are a matter of professional judgement.42 The National Audit Office report highlighted the need for the Department to consider project risks more fully, including reflecting these independent project costings in its own forecasts.43 Type: conclusion | Number: 16 | Response status: not_addressed Government response: 4.1 The government agrees with the Committee’s recommendation. Target implementation date: December 2023 4.2 Forecasting across ten-years is inherently uncertain. In a complex plan with many large programmes, forecasts change as delivery schedules and cost estimates mature. Improving forecasting can