The Department for Work and Pensions' statistics for fraud and error within the benefits system in 2014/15 estimate that £3.2bn was overpaid, equating to 1.9% of its total expenditure. However, the figure within housing benefit is actually much higher, at 5.7% of expenditure. Of course, many claiming housing benefit also claim council tax reduction too.
Although the Department for Communities and Local Government are yet to produce figures on this, we can draw parallels with the Audit Commission's figures into the financial loss attributed to single person discounts, where between 4% and 6% are fraudulently claimed.