Firstly, they can not harm you, dont panic! they are more scared of you than you are of them. Having said that, they are creepy and unfortunately they are a ****** to get rid of because they hide in tiny places and breed like crazy, so if you kill a lot, there are still loads left! Making sure the place is clean will help, they live where they can find food, so clean every scrap of grease, crumbs etc from every surface and nook and cranny. Is it a council flat? If so then their exterminator should clean them out before you move in, if not, then find a pest controller in Yellow Pages and get the job done professionally, tyring to eradicate them yourself may be cheaper, but I doubt it will be successful.