At Manchester if you don't do one of their SQT sessions for 6 months then it's almost back to square one: you have to gain accreditation again. To race in Manchesters track league you do not need accreditation, you can ride them without, same as at the track masters competitions & such. Having accreditation is beneficial though, it gives you the skills, confidence & know how.
Currently if you are accredited at one track you are not automatically accredited on other tracks. From what I have heard they are working on this, & hopefully it will make it easier to get on SQTs at other velodromes across the UK.