Unemployment unexpectedly rose by 46,000 to 1.47 million in the three months to December, official figures show.
It was the largest rise in the jobless total since early 2013 and the first time it has jumped since the summer of 2016.
The figures from the Office for National Statistics (ONS) sent the pound half a cent lower against the US dollar to just over $1.39.
They showed that the unemployment rate also rose, from 4.3% to 4.4%.
Pay growth turned higher – with average weekly earnings, excluding bonuses, up by 2.5%, an improvement on the previous figure of 2.3%.
But wage increase continue to lag behind inflation, meaning that in real terms pay fell by 0.3%.
Unemployment has been generally falling since a post-recession peak in 2011, apart from a handful of increase, most recently in 2016.
There is no evidence yet as to whether the latest fall is another apparent blip or the beginning of an upturn in joblessness – at a time when wider economic growth has been slowing.
Despite the latest increase, the jobless total is 123,000 lower than a year earlier.
Meanwhile the number of people in work continued to rise over the last three months of 2017, up by 88,000 to 32.15 million.
That apparent discrepancy, at a time of rising joblessness, is explained by the fact that the number of economically inactive people – those not seeking or available to work – fell in the period.
Employment minister Alok Sharma called the employment rate of 75.2% – down from 75.3% a month before – an “incredible achievement”.