The UK's flexible working strategy has developed progressively since 2000, reflecting changes in the economic, political and social climate. Research has shown employees to be concerned about the effects of flexible working on career success. This paper (N=266 & N=1093) examined male, female, managerial and non-managerial evaluations of employees who either used flexible working practices, worked long hours or worked regular hours. It also compared attitudes towards employees and their perceived success as a function of the reason as to why they used flexible working practices. Results showed individuals working the longest hours were perceived to significantly outperform all those who worked regular hours or who took part in some kind of flexible working option. Women with caring responsibilities were consistently viewed as less productive and more likely to leave their employment than men. Findings on promotion show overwhelming bias towards long hours being compatible with career success. Despite the positive effects on work performance, the effects of working long hours are recognised as detrimental to work-life balance. The implications for women in the workplace and work-life balance policy are further discussed.