There are no subject requirements, outside of taking an academically demanding course of study. People successfully apply with both STEM subjects and essay subjects. However they normally prefer traditionally academic courses, and I would strongly recommend not taking more than one applied/vocational/creative arts A-level, or similar which is not primarily assessed by written exam.
History is often considered one of the best preparations in terms of analytical essay writing, but is not required by any means. Taking all STEM subjects would also be fine, as above, although you may find it a little more challenging to adjust to the different style of assessment at the very start - but I've not seen any data suggesting students taking STEM subjects do any worse overall in their degree classifications.
The most important thing is to take the three subjects you will do best in - these are often the ones you enjoy the most as well. Apart from avoiding taking multiple creative arts or vocational/applied A-levels then any courses will be suitable.