I may be wrong, but I'm pretty sure you need to pass your vetting before the option of becoming an OSG waiting on your POELT.
Best of Luck to you.
My email stated
Your details and accreditation notification will now be sent to the Ministry of Justice administration centre. They will hold your details on the accreditation list and contact you as soon as you are matched to a vacancy at your chosen Prison so that the vetting and security process can be started where required.
Your accreditation is only valid for 12 months, if after the 12 month period you have not been matched to a vacancy at your chosen Prison your accreditation will be withdrawn. Candidates who are not allocated to a Prison vacancy during the 12 month period are required to reapply to a new campaign.