✔ 最佳答案
Hitler managed it because of the weak Weimar Republic constitution and the Nazi Party's private army, which made everyone afraid to oppose him. Having been elected in 1933, he managed to get an Enabling Act passed which gave him power to rule by decree. You've had this explained in detail when you asked about it twice before and I'm not going to go through it all again.
The British constitution has weak points because so much isn't written, which could potentially allow a British party to do the same thing.