Naturalisation. Full capacity requirement
If you apply to naturalise as a British citizen, you must satisfy the full capacity requirement. You must be “not of unsound mind”.
That does not mean that your application will be refused if you have a disability. It means that you must be able to understand the purpose of your application for citizenship.
You do not need to understand the citizenship procedures, actually most people of sufficiently sound mind do not know the law. You just need to understand that you want to be British and that this is what you apply for.
If you have a mental health condition or learning disability, and if it is in your best interest, the requirement may be waived. In such a case, you will not be obliged to make the oath and pledge, or to attend the citizenship ceremony.
If you want to apply for British citizenship or for a British passport and need specialist advice, feel free to contact me. Please note that I am an accredited immigration adviser, not an employee of the UK Visas and Immigration. I charge fees for the advice provided.