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The total fell from 232,900 to 207,213, despite an overall rise in the workforce, an analysis of government employment statistics has revealed.
The decline represents an acceleration in a long-term trend which has seen the proportion of women in the profession fall from 26% to 20% since 1999. It has led to renewed fears that women are still being put off by IT's "techie" image and unsocial working hours, despite campaigns to stress the importance of management and communication skills.
IT directors said the trend could spark a skills shortage as the jobs market recovers. "Quite soon we are going to go up the hiring curve. If we are not attracting 50% of the workforce, we will be experiencing a skills shortage," said Maggie Miller, Sainsbury's business transformation director.
"It is certainly worrying if the talent pool decreases," said Jenny Sener, IT director at OCS Group.
Research by E-Skills UK shows that women are deterred at an early age, with 94% of schoolgirls saying they would not consider it as a career. But the problem has been exacerbated by the difficulties women face returning to work after career breaks to bring up children, said Karen Price, chief executive of E-Skills UK.
Philip Virgo, former director of the now defunct Women In IT campaign, said the lack of tax breaks for childcare in the UK was accelerating the decline.
Miller said women often have the softer skills employers are looking for in IT staff, including team working, the ability to communicate with customers and a strong focus on using IT to meet a business purpose. "If the UK industry is to be at the leading edge, it needs a lot more than technical skills - and quite often those skills are associated with women."