In summary, you need a handrail or banisters where the drop is over 600mm. They must be over 900mm high and as said in a previous post, you must not be able to get a 100mm sphere between the spindles.
You need to understand the context, and the regulation will differ for domestic or commercial stairs. Also if you are replacing stairs or adding new ones.
For information specifically on handrails, banisters and balustrades, please have a look at this project for more in depth information:
https://www.diydoctor.org.uk/projects/ba ... drails.htmThe building regulations for stairs (Part K) have been summarised here so that you can understand what is required for your stairs, and not just the hand rails:
https://www.diydoctor.org.uk/projects/bu ... tionsk.htmThankfully these regulations are not as daunting as they sound, so you can get a very clear understand quite quickly.