The amount of rate debt written off in Northern Ireland has increased by 50%.More than £150m in household rates remains outstanding - owed by those who cannot or will not pay.The write-off peaked at £15m last year and is expected to rise even further this year.With deep cuts made to the budget the executive gets from the Treasury, the revenue raised through household rates is increasingly important.More than £1bn is collected in rates each year.Because of the current economic climate, the amount of debt that has been written off is increasing.It has risen from £10m to £15m this year - an increase of 50% and is set to rise even further.The number of people who have had to enter into special arrangements to pay their rates has more than doubled.