Unless you were told before you took your NVQ2 that you would be asked to repay it if you left, or even better were given written confirmation of this or signed something to that effect, they would be hard pushed to force you to pay if you left. If they made a deduction from your final pay it would be an inappropriate deduction and you could bring a claim against them for doing this.
If you did know before you undertook the training that you would have to repay it if you left then you�ll have to repay it. Even training contracts like this have a time lapse (i.e. leaving within 2 years of completing the training) so I suspect your employer is trying it on.
It sounds like you�re ready to leave this employer. Move on. If they treat you badly contact the CAB for local advice. Document everything and put your complaints to them in writing calmly and instigate a grievance procedure.