According to figures from the Office for National Statistics, by the GMB union, workers in Bracknell Forest are earning an average of £18 a year less than in 2008.
Wokingham's average earnings increased from £34,819 to £35,739 in the same period, and there was also a rise in the Royal Borough of Windsor and Maidenhead - which includes the Ascot area - from £42,436 to £43,113.
David Knowles-Leak, chairman of the Thames Valley FSB, said the recession has resulted in a real turn-down, with people not getting discretionary benefits and more part-time work being created.
He added: "Why it's gone up in boroughs but gone down in Bracknell - I don't know."
Despite Bracknell Forest's fall, the average change across the UK is up 2% - from £26,137 in 2008 to £26,664 last year - but this represents a 12.8% drop in real terms taking into account the current costs of goods and services.
Reading had the highest growth in Berkshire, rising from £27,460 to £29,502.
However, West Berkshire had the biggest drop in the whole of the South East, with workers earning 20.4% less than in 2008, dropping from £33,137 to £31,269.