You need to test at least every 6 months, but in order to test you have to be assosiated with a VTS, the VTS has to do a quality control check with you every month. So ideally you have to test every month.
That's easier said than done, because if you test every month for a VTS, they are then accountable if you make a cock-up, so you will have to convince them that you are reliable and good at your job (which I'm sure you are).
If you don't intend to test properly for the forseeable future, then why are you concerned about your MOT license. Just do a refresher course when you are ready to resume testing full time.
I am just about to leave my job as a tester to work in a garage that doesnt test . Can anyone tell me how often I need to test to keep my license - and is there any VT stations in the Coventry area who would like a part time (very!!) tester ?