The UK government spent at least £4.4bn ($5.6bn) on Brexit planning in the run-up to Britain’s departure on 31 January, according to a watchdog.
Government staff numbers working on Brexit peaked at 22,000 last October, when Britain came close to leaving the EU without a deal.
A report by the National Audit Office (NAO) on Friday highlighted the enormous scale of government resources required for a challenge with “little or no historical precedent.”
Costs borne by the taxpayer include £1.9bn on staffing and £1.5bn on building new systems and infrastructure to plan for wide-ranging changes affecting many areas.
All 18 central government departments incurred costs, with 300 different “work streams” dealing with different issues.
But three departments accounted for 70% of the costs, according to the NAO. HMRC spent £748m, the Home Office spent £803m and the department for environment, food and rural affairs (Defra) spent most at £871m.
Defra’s costs include planning new checks on animal and plant imports, regulations for chemicals and farmers’ subsidy scheme to replace EU arrangements. The Home Office has invested in Britain’s border systems and the EU settlement scheme. HMRC has spent funds on VAT and customs systems and contingency planning for no-deal border disruption.
But Meg Hillier, re-elected chair of the Commons public accounts committee and a Labour MP, claimed the public had been “left in the dark” about the detail of much government spending.
“Data is limited, and the Treasury seem unconcerned by the lack of transparency,” she said.
Gareth Davies, head of the NAO, said the report provided the first clear picture of government Brexit spending. But he said compiling it had highlighted “limitations” in how the government monitored spending on Brexit and issues crossing departments more generally.