THE UK Government has been slammed for a lack of transparency after it was revealed Brexit has cost the taxpayer a minimum of £4.4 billion in additional government costs.

Whitehall spending watchdog, the National Audit Office (NAO), said that between the EU referendum in June 2016 and March 31 this year, government departments will have spent at least £4.4bn, while £6.3bn was allocated by the Treasury for Brexit preparations.

They included planning for both deal and No-Deal scenarios, with £2bn specifically earmarked for No-Deal preparations in 2019-20 – though this was scaled back after the prospects of a hard withdrawal receded.

But overall, the NAO said the figures represented a "minimum estimated level of spend" due to "limitations" in the data provided by departments.

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The chairman of the Commons Public Accounts Committee, Meg Hillier, said: "The public has been kept in the dark as to what the Government has been doing.

"Data is limited, and the Treasury seem unconcerned by the lack of transparency."

Of the money spent, £1.9bn went on staffing costs, £1.5bn on building new systems and infrastructure, and £288 million on bringing in expertise and external advice.

At the peak of activity, in October 2019, there were 22,000 staff working on Brexit preparations, including 1500 who had been moved within government to prepare for a possible No-Deal exit.

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The head of the NAO, Gareth Davies, said: "In preparing for EU exit, government departments planned for multiple potential outcomes, with shifting timetables and uncertainty.

"Producing this report has highlighted limitations in how government monitored spending on EU exit specifically, and cross-government programmes more generally."