The law now gives people with disabilities some protection against discrimination. This makes it harder, though not impossible, for employers to exclude you from the scheme (in practice employed people with a disability are less likely to meet the qualifying criteria for auto-enrolment).
Employers can only do this if they can show there is substantial extra risk of you taking early retirement due to ill health. You can also be deprived of some benefits on the same grounds, though you will still have to make the same contributions.
If you are excluded from the scheme you have no right to the employer contributions that would have been paid on your behalf. It is illegal for you to be excluded from a scheme or some of its benefits at any time except when you first ask to join. You cannot be excluded if you become ill or develop a disability after you have been accepted as a member.
You normally have to wait until you’re at least 55 before you can start getting your pension, but if you have to retire early because you're ill or disabled you might be able to get your pension earlier.