The estimated cost of decommissioning the AGR stations, plus the PWR at Sizewell B, increased from £12.6 billion in 2004–05 to £23.5 billion in 2020–21 in real terms. We asked the Department why the estimated cost of decommissioning the AGRs had increased to such an extent. The Department asserted that decommissioning costs will never be entirely certain as projecting decades into the future carries a degree of risk. It emphasised that circumstances will change and therefore the decommissioning estimate number could move up or down.14