Reliance Employment - Holidays

Has anyone had any experience of working for Reliance, an agency? I’m currently on a placement for them, been there 8 weeks, and have a slight issue. It seems, after asking about holiday pay, I was told “we don’t pay holidays, if you’re not working you’re not earning”. Every other agency I’ve worked for has paid holidays, and as far as I know, I’m entitled to paid holidays, so what’s their game, how do they manage to get away with it? And what is the best way to deal with it? Leaving is one option, but I’m 8 weeks in to a placement that could become perm so I’m reluctant to go down that route.