Your security clearance lasts for a maximum of three years. With staff working from home, it’s quite easy to let your security clearance lapse without you realising it. However, if it does lapse, you will not only lose access to the Parliamentary estate, but you may also lose access to the Parliamentary network – i.e. your emails, the intranet, etc.
Go and have a look at your pass and check if it’s still in date. If you don’t have a physical pass, but have security clearance for network access, you can check the date on the email you were sent when clearance was first granted (you did keep it, didn’t you?)
If your clearance is due to expire soon, or has already expired, consult the relevant page on ParliNet.