Many moons ago (pre CSA) a friend of mine ended up in court for non-payment of maintenance. His ex-wife was now living with someone esle and he felt he should not be paying anymore.
The judge agreed with him, but said that technically he had broken the law and he had no option but to give him a custodial sentence - 14 days in Pentonville.
He also reduced the maintenence to sixpence a week!