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The FDA union, which represents those working in government, said in a statement that senior civil servants are unhappy because "the challenges of Brexit and existing Government priorities are pushing the service to its limits, while the SCS work more hours for falling real-terms pay."
FDA General Secretary Dave Penman added:
"Fresh from reducing the size of their departments, the SCS is now tasked with implementing Brexit on top of all of the Government's existing priorities. To quote one member, '…the country needs a civil service that is optimistic, energised, proud, confident and ambitious - what we have is a senior civil service that is thoroughly dispirited and demotivated.'
"Some haven't seen a pay rise in a decade, all have seen their pay cut in real terms by around a quarter. The strain of the pay freeze and staff reductions is taking its toll. The previous Chancellor's policy of public sector pay restraint has led to a demoralised workforce and a civil service now reliant on expensive contractors and salary premiums for new hires."
What is also interesting is that the FDA claims a quarter of the civil service are ready to leave "as soon as possible."
This comes as the latest in a line of issues Prime Minister Theresa May's government faces in dealing with exiting Britain about of the EU.
Britain voted for a Brexit by a slim majority on June 23 and, since then, there has been much speculation on when May will trigger Article 50 and therefore start the two-year negotiation period. March 2017 is the current target date but a Supreme Court case will rule in January 2017 whether she will have to get permission from parliament to do this. This could slow things down.
May says she will not give a "running commentary" on how negotiations are going but this has led to criticism - including that from Sir Ivan Rogers who unexpectedly quit as the British ambassador to the European Unionon January 3 - that she does not have a concrete plan.
Rogers' resignation letter contained thinly veiled attacks on the way the government is handling the Brexit process, including the allegation that "serious multilateral negotiating experience is in short supply in Whitehall."
He also called on former colleagues to challenge "muddled thinking" and "ill-founded arguments" during the Brexit talks.
The FDA statement also follows various statements about SCS being pushed to breaking point.
In November, the former head of the Foreign Office in Britain, Sir Simon Fraser said the British government's lack of a clear Brexit plan is prompting senior officials to think about quitting.
Sir Simon said during a House of Commons Committee hearing that "civil servants don't feel they have clear political direction at the moment," and some are thinking of quitting their posts.