Just my 2 centavos
As it stands right now the UKBA will want to see at least Income Support levels.
That means a minimum of £111.45 per week of disposable income. After payments for rent/mortgage/loans and iva etc
Means completely free to spend on whatever.
Maybe the IVA payments do not allow that much "free income" each week.
Without the required income UKBA will have great difficulty to grant the visa.
Looking out to the future, the UKBA may introduce financial thresholds based on gross income only. In which case you may stand a better chance.