The losses were reportedly announced at the organisation's annual general meeting (AGM) on Wednesday.
In addition to the commercial losses, it is also reported that the society's reserved were shown to have fallen to less than £8 million from £16 million five years ago.
According to Computer Weekly, the BCS's retiring chief executive David Clarke advised that decline was driven by investments made as a means of attempting to improve the organisation's commercial performance.
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The BCS aims to promote, "wider social and economic progress through the advancement of information technology science and practice." Despite its goal, professional membership to the organisation has reportedly remained static at 44,000, with total membership numbering 74,000.
The AGM was said to see a low attendance and number of disagreements, specifically to do with the supposed lack of a clear plan for the BCS to tackle its loss-making commercial activity and the society's lack of profile in the media.
In response, outgoing president Roger Marshall was reported as saying, "The media don't like it when we point out that very often failures are not an IT issue, but a management issue."