Opting out means you leave the Scheme within one month of being enrolled by your employer. You stop making contributions and so does your employer. You don’t build up a pension for yourself in the Scheme.
Your employer will refund any contributions you’ve made since the enrolment date, as long as you opt out within one month of being enrolled (or re-enrolled) in the Scheme.
If you opt out, it’s likely you’ll be re-enrolled in the future. This is because your employer’s legally required to check whether there are any eligible employees who aren’t in the Scheme every three years, and enrol them if they are. You can opt out again if you want to.
The opt-out period is set by the government and enforced by The Pensions Regulator.