The UK government's domestic agenda will have to take a back seat as the civil service deals with Brexit, the head of the senior public servants union warned on Friday (20 January).

Dave Penman, general secretary of the FDA, told IBTimes UK that senior civil servants are prioritising the issue because of a lack of resourcing.

Penman, who represents around 19,000 members, claimed that the civil service was "constantly being asked to deliver more for less".

"Something has to give here," he warned. "You've either got to make some choices around priorities or you've got to understand what('s) the impact of continuing to ask more for less from our members."

Penman said the Department for Exiting the EU and International Trade have seen funding hikes, but other ministries, such as the Department for Environment, Food and Rural Affairs, are facing larger workloads without the resourcing to match.

The result is that around 10% of senior civil servants are effectively working seven day weeks, according to FDA surveys.

Penman also highlighted pay as an issue. Public sector workers, including civil servants and NHS workers, have faced a pay freeze since 2010 and an annual salary rise capped at 1% from 2012.

"Pay has been declining for a decade now and there's no light at the end of the tunnel, resources have been cut for two parliaments in a row by about 20%, you've then added a huge challenge on top of it," the general secretary said.

But Penman denied claims that Whitehall officials, which is portrayed as a pro-EU institution, are resultant to tackle Brexit-related work or join David Davis' Department for Exiting the EU.

"Brexit is the most interesting thing to do in the civil service," he said. "If you were looking for a career and you are bright young thing, you would want to be at the heart of this because it's a really interesting intellectual challenge."

Penman's comments come just days after Theresa May's landmark Brexit speech at Lancaster House, London.

The prime minister announced, among other things, that the government would not seek to maintain the UK's membership of the EU single market.

Penman had called for more clarity from the Conservative premier unveiled her 12-point Brexit plan.

"It's too early to judge yet whether the prime minister has given the civil service the clarity it requires to negotiate," he said.

"She set out more but that's really about the political pressures that she's been under rather than the reality of what a set of negotiations is going to be.

The union chief also urged May and her ministers to make sure their political objectives are clear to civil servants throughout the Brexit process.

When asked about an Institute for Government report which warned that Whitehall "urgently needs" to be prepare for the Brexit negotiations, May told the Liaison Committee in December: "I am afraid that I am tempted to say, in answer to your question.... that I am not at all surprised when former civil servants suggest that we need to employ more civil servants."

The prime minister plans to invoke Article 50, the mechanism to split from the EU, by the end of March. The move will trigger talks with Brussels which are expected to last around two years.

But the Supreme Court is still yet to rule on whether MPs or peers should have a vote on invoking Article 50. The justices will announce their historic decision on Tuesday.

A Cabinet Office spokesperson said: "The prime minister has been clear that the government's manifesto commitments will be delivered alongside our exit from the EU.

"The civil service has shown on countless occasions that is it a resilient and adaptable organisation, and is working hard to make sure that all of the prime minister's priorities are being delivered."