The union said its members in 124 government departments and other bodies will walk out on February 1.
Hundreds of students will not be in school as the teaching strike continues today.
Shares rose in London after a rollercoaster day.
Universities could face strikes after union members voted in favour of action.
The influential S&P Global/ CIPS flash UK composite purchasing managers index showed a reading of 47.2 in October, below September’s 49.1.
Lord King of Lothbury outlined the challenge for the next prime minister to confront high inflation.
Schools have been ‘cut to the bone’ by funding cuts, the head teachers union has said.
A Cambridge University study found that key ingredients were often missing from the training teachers received.
The Labour leader also urged disillusioned Conservative MPs to put the interests of the British people first.