Many cheap unbranded generic chargers which are imported to the UK are quite cheap which is primarily why they are so popular. These chargers are unsafe and pose a potential fire hazard. This means that in the production process many safety policies are disregarded which means that they are unsafe to use. Many fires have occured in the Uk and some examples are:
http://www.dailymail.co.uk/news/article-2600682/Mobile-phone-catches-fire-owner-leaves-charge-asleep.html
http://www.dailymail.co.uk/news/article-2626079/House-fire-killed-nine-week-old-baby-girl-two-little-boys-aged-7-9-aunt-grandmother-started-faulty-phone-tablet-charger.html
In these links you can see the serious risk posed to everyone using a cheap generic charger.