Scrolling through Instagram, you're bound to come across an influencer wearing an outfit from one of the internet's many fast fashion retailers. Pretty Little Thing and Missguided offer loads of clothes at really low prices - and they update much quicker than the high street. But how are these online retailers impacting the environment? And what role does social media play in the "wear it once" trend? MPs released a report last week outlining their worries about fast fashion's effect on the environment.