A slight error in the estimate or buy a new calculator?

Report in Live Rail Feb 2017 (Journal of the Southern Electric Group)

“The Department for Transport has discovered that the £20 M originally allocated was far from adequate, so is providing £300 M for improving the resilience of the Southern & Thameslink network.”

That is an error in the “estimate” of £280 M- ( 1400% ).

Anybody dismissed, shot at dawn or hung from a lamp- post- course not- the taxpayer will provide!