Toiling away in the background on a shoestring budget, some 300 civil servants in a hastily assembled new department are scrambling to deal with Brexit, the biggest administrative challenge in Britains post-war history.

Staffed with officials mainly poached from other ministries, the newly minted Department for Exiting the EU (DExEU) was founded only three weeks after the June 23 referendum that triggered Britain's divorce from the EU.

Led by 68-year-old Conservative MP David Davis, the department is located at 9 Downing Street -- right next door to Prime Minister Theresa May's office.

The department's headcount is now "just over 300," director general Sarah Healey told AFP.

"It's the amount that we have planned to do the job", Healey said, dismissing worries that it might not be enough but admitting the ministry is "still growing".

Even before getting landed with the huge administrative headache of Brexit, the British civil service was already on the back foot after austerity cuts.

"The civil service faces its biggest challenge since the Second World War," and yet its "workforce is the smallest it has been in 70 years," the Institute for Government said in a recent report.

Since 2010, the number of civil servants has dropped by 18.5 percent to fewer than 400,000.

In 1944, the number was three times as high.

Britain's former ambassador to the EU Ivan Rogers, who quit in January warning that negotiations on a new trade agreement could take years, said the challenge for Britain was on a "humongous scale".

'Turf war'

On top of the numerical and financial challenge, another problem has been to find sufficiently qualified people and Britain has had to trawl abroad to find the necessary talent.

For example, since its 1973 accession to the European Economic Community, Britain has not negotiated any international trade deals because those fall under the purview of the European Commission.

Faced with a lack of British negotiators, the new Department for International Trade (DIT) has enlisted professionals from Australia, Canada and New Zealand.

The National Audit Office, Britain's budget spending watchdog, said in a report last week that leaving the EU would "further increase the capability challenges" for the civil service.

"Government projects too often go ahead without government knowing whether departments have the skills to deliver them," he said.

The audit office said the government needed to show "greater urgency" in filling the skills gap in Whitehall.

But Anand Menon, professor of European politics at King's College London, played down worries of a skills shortage.

"Britain has generally been quite good at negotiating in the European Union so there's no reason that we can't continue to be quite good at negotiating with the European Union."

However, Menon added: "There will be tensions between different departments and tensions between different ministers about the priorities" in the negotiations.

The Institute for Government made the same point, saying that "time and energy was inevitably wasted in turf wars" between the Brexit ministry, the trade ministry and the foreign ministry over strategy.

The risk now is that the task of at least two years of Brexit negotiations could prove so challenging that it will hamper the rest of government business.

Menon warned: "Brexit will consume Whitehall".