Torsion bar too soft

[Slam Wagon]

Ok so ive lowered my hdi estate some time ago and its always been really soft, i did it the pikey way as the bars were not moving if i tried it properly. After fitting my new wheels i need to firm up the back end, ive already fitted stiffer shocks and although theyve helped its not enough. If i undo what ive done to the torsion bars and do it properly will it stiffen the suspension? Or is there a way to stiffen it without undoing it all and then doing it properly? I want to keep the ride height i have and just firm it up.

Thanks

Ian