well when i got the bike off tartys i told them about it and they said "Sounds as though you have it not quite tight
enough or it isn't installed correctly. Please ensure the hanger and
tensioner are all setup correctly. A good way to do this is to sit on
the bike backwards as you tighten the bolts, so the axle is all the
way into the dropouts." i got it set up properly down my mates and he had a go and it came out again when it was tightened up
ah right well its all sorted now haha and i might be coming up MK for like a week in the summer next year bringing the bike up just to ride with new people and ride a new area