In principle, you have to agree to security vetting before it can proceed. If you don't agree - for whatever reason - you don't get vetted and you are also unable to do work requiring that sort of pre-check.In terms of working in an organisation that has a high number of SC/DV/strap staff, it can never get to the situation where 'everyone' is covered, some temp staff, foreign nationals, or people who don't want to, will remain 'uncleared', and x-site rating is maintained through other (mostly physical, ie locks and access door methods).Bottom line is you 'might' not progress your career as fast if you can't work on the MoD/secure projects if that's your firm's speciality, but nor can that make you take part in a vetting process you don't want to.