Just saw their post on Instagram.
Basically, purchase two sale items in store and get a third sale item free!
A previous post on their Instagram also states that the in-store sales are 50-70% off.
Starts tomorrow (9th October 2014)
Runs for a limited time only.
As a sales assistant at topshop/topman, I can say that 70% off any item is pretty much the biggest discount you'll ever find on their products. So if you bought all three items at this price of 70% off, it's a real bargain given the third is a free one. It's also the first year I've seen them do this promotion, so if you're hesitating because you think they may have another sale like a FURTHER 25% off or something, don't, it's a good deal :D