I looked into brands that use sweatshop workers last year and it's a long list - M&S (though they were apparently shamed into promising that workers would be paid living wages by 2015 so I hope that happened) H&M, Gap, Matalan, Primark, Nike, Adidas, Next, Topshop, Warehouse, Mango, Debenhams, Oasis, Miss Selfridge, and of course Apple and Disney.
Modalu were probably targeted due to the DMs stalker like obsession with Pippa Middleton for a few years.
But I would like to buy ethically more often. It's just hard to know which are the truly ethical (and affordable...) brands.