Couldn't find an example of that in the UK from googling so hopefully Steven. can come back, however two examples of women being put in men's prisons for very different reasons:
Canada has put a completely non-violent (cis) women prisoner in a mens prisons for 'space reasons': http://www.cbc.ca/news/canada/newfoundland-labrador/beatrice-hunter-now-...
In this US case a (cis) woman was put in a men's prison due to severity of the conviction: http://www.nydailynews.com/news/world/female-ice-cream-killer-moved-all-...
Have you got a link for details on this please?