In May 2024, the House of Commons Commission endorsed a number of changes to vetting policies, including that all Members’ staff funded by IPSA must be security cleared and this will come into force on 1 April 2025.

Please see this news article for further information: https://parlinet.parliament.uk/information-resources/news-newsletters-notices/news/2025/february/changes-to-members-staff-security-vetting/

and also this w4mp guide to security clearance for Members’ staff

https://w4mp.org/jobs-listings-events/jobs/members-staff-security-verification-questionnaire/