Prudie- here is a quote from a leading employment law solicitor Corinna Ferguson. The Smith decision was about length of hair and is not terribly relevant here and the subject of being forced to wear make up in work has never been fully tested in a UK court however, it appears to be the case that it can certainly be considered harassment in certain cases.
''The Smith decision was handed down in 1996 and followed a line of similar decisions which have been much criticised for approving gender stereotypes. Thirteen years on it is possible that courts would be more open about what constitutes appropriate work dress. But in any event it seems to me that a policy requiring women to wear make-up differs in a number of respects from a policy banning men from having long hair. Although make-up can be removed and therefore does not necessarily govern an employee's appearance away from work, there are two features which I think make it more objectionable than the hair policy. First, it requires women to spend more time and money on their appearance than men, which could – if more than a very trivial difference – "unbalance the treatment of men and women as to amount to less favourable treatment". But more importantly it seems to me there is something particularly demeaning about the notion that women must wear make-up in order to look acceptable. There is nothing wrong with a policy which demands that all employees look tidy and presentable, but saying that women cannot do so without wearing foundation, blusher, eye shadow, mascara and lipstick – and there surely would have to be quite specific rules if the policy was to mean anything – is outdated and deeply offensive to many women. In an extreme case the enforcement of such a policy could even amount to harassment.''