Preparations for the United Kingdom's exit of the European Union cost British taxpayers 4.4 billion pounds (€5.1 billion, $5.7 billion), according to the UK's National Audit Office (NAO).

In the first detailed estimate of the cost of the Brexit, the NAO on Friday estimated that the British government spent about 70% of the 6.3 billion pounds allocated to cover the cost of preparations between the June 2016 referendum and March 31 of this year. The allocated money accounts for the possibility of the UK and EU not reaching a trade deal before the end of a transition period that expires at the end of 2020.

The EU's chief Brexit negotiator, Michel Barnier, warned of "serious divergences" in expectations between the EU and the UK as the first round of post-Brexit trade talks wrapped up on Thursday.

"To be completely frank with you ... there are many divergences, and they are very serious divergences, which is probably quite natural," Barnier said.

Read more: What do both sides want?

The NAO said most of the money was spent on staff costs (1.9 billion pounds), building new infrastructure (1.5 billion pounds) and paying for external advice (288 million pounds). Some 22,000 government officials were working on Brexit at the peak when the UK was close to leaving the EU without a withdrawal deal in October 2019.

More than half of the money was spent by the Environment Agency, the Department of Food and Rural Affairs and the Home Office.

"This report provides, for the first time, a clear picture of how much government has spent and what that money has been spent on," said NAO head Gareth Davies.

He added that the report "highlighted limitations in how government monitored spending on EU exit specifically, and cross-government programs more generally."

The NAO said their estimate only focused on the cost of government preparations, not on future expenses such as the 39 billion pound divorce agreement agreed with the EU.

A member for more than half a century, the UK became the first country to leave the bloc on January 31. The UK is currently in a transition phase until the end of 2020 in which EU rules still apply as London and Brussels try to hash out a trade deal.

dv/sms (AFP, Reuters)

DW sends out a daily selection of hard news and quality feature journalism. Sign up here.